Báo cáo lâm nghiệp: " from the simple application of a mixture of to more gibberellins integrated explanations"

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Promotion of flowering in conifers: from the simple application of a mixture of gibberellins integrated explanations to more M. Bonnet-Masimbert INRA Station dAm6lioration des Arbres Forestiers, Ardon, 45i60 Olivet, France Introduction factors interact extensively. In fact, in order to get a more reliable response, the hormonal treatment of conifers has gen- Flowering induction in trees is still an erally been associated with different kinds important problem for both the supply of of cultural treatments. Thus, in the field, it seed and breeding programs, which have is generally possible to enhance the natu- to face the long juvenile phase and irregu- ral flowering cycle of a tree in good years lar flowering so common in most forest or in good flowering clones but it is still dif- trees. Many recent reviews indicate clearly ficult in off years or with recalcitrant that induction of flowering is now possible clones. In greenhouses, it is possible to in many conifers in a more or less juvenile have a better control of some of the envi- stage (Owens and Blake, 1985; Pharis ronmental factors and to obtain more and Ross, 1986; Pharis et al., 1987; Bon- reproducible results. This is one reason net-Masimbert, 1987; Bonnet-Masimbert why containerized indoor orchards are and Zaerr, 1987). In most cases, the treat- now proposed as a favorable alternative to ments are based on the use of gibberellins conventional soil-based orchards (Ross (GAs), especially the mixture of GA4 and et al., 1985). GA7, which were demonstrated to be the active gibberellins for Pinaceae species The details of the various applied treat- (Pharis, 1975). ments will not be discussed in this review. However, the problem of stimulation and They are amply documented in the pre- of flowering in forest seed viously quoted reviews. Owens and Blake regulation orchards is still far from a general solution. (1985) presented a general review of all the reproductive processes from floral ini- These difficulties are due to the fact that, tiation to seed development. Pharis et al., in opposition to photoperiodic or thermo- (1987) paid special attention to the effect periodic herbaceous plants, the flowering of woody perennial species involves of exogenous applications of GAs and cul- tural treatments on variations in endo- undoubtedly a multifactorial regulation genous GAs. They discussed the specific where environmental and physiological
no low polarity GAs after root and not pharmacological action of less revealed whereas they were found up to 6 polar GAs on flowering. Also, the relation- flooding, weeks after one stem injection of GA4/7 ship between flowering and shoot growth or bud vigor was discussed. Ross and (Pilate, 1987). Both treatments produced the same floral response, which might Pharis (1987) presented recent concepts mean that compounds other than GAs are of sex expression in conifers. Other plant also able to stimulate flowering or that growth regulators (PGRs) were consid- flooding produced a deferred induction, ered by Bonnet-Masimbert and Zaerr possibly by retarding the differentiation of (1987). Practical treatments (i.e., tech- lateral apices as observed after root prun- niques and doses of PGRs) are discussed by Bonnet-Masimbert (1987) and finally, ing (Owens et al., 1986). Ross (1986) reviewed the effect of tem- On the contrary, Pharis et al., (1987) perature on reproductive processes. reported increases of less polar GAs after root pruning, girdling, nitrogen fertilization This paper will mainly report on relation- and drought. GAs seem to vary promptly ships between GAs, other PGRs, growth after either girdling (Wesoly, 1985) or heat characteristics of shoot and roots and treatment (Chalupka et al., 1982). In Nor- some of the cultural treatments which can way spruce, Dunberg et al., (1983), interfere with flowering. Special emphasis demonstrated that covering the plants with will be given to the present development a plastic film reduced the metabolism of of studies on flowering at the INRA re- [ into other GAs. In Douglas fir, H]GA4 3 search station (Ardon, France). Pharis ef al., (1987) also observed that, 10 weeks after root pruning, a much higher proportion of [ was unmetabolized H]GA4 3 endo- Effect of cultural treatments on in pruned trees than in control trees (45% genous growth regulators instead of 28%). This indicates a long last- effect of the treatments which create ing a polar GAs. Recently, build up of less rapid Gibberellins using immunological analysis instead of bioassays, Doumas et al., (1989) demon- Many of the commonly applied adjunct strated on 3 year old cuttings of Douglas treatments can be interpreted as affecting fir, 17 days after stem girdling, a drastic root growth. One of these treatments, increase of some GAs, mainly a GA3-like flooding of roots, stimulated flowering and peak, but no increase of less polar ones. synergized the GA4/7 effect on Douglas fir Only trees having received GA4/7 ex- (Bonnet-Masimbert, 1982; Bonnet-Masim- hibited significant levels of these GAs. bert and Zaerr, 1987). Using rhizotrons, These apparent differences between the flooding was demonstrated to quickly stop experiments may be partly due to rapidly root growth and the same was also ob- varying levels of GAs, but they confirm that served after stem injection of GA4/7 (Bon- most cultural treatments which have so far net-Masimbert, 1987). This suggested that been analyzed have a direct effect on the reduced root growth might be favorable to level of GAs in the shoots of treated trees. flowering. On tomato, root flooding reduced the Cytokinins general level of GAs in the roots, shoot and sap (Reid and Crozier, 1971). On the work on many herbaceous From Douglas fir, quantifying GAs by enzyme- it appears that the levels of dif- plants, linked irnmunosorbent assay (5A), . Fl- 1
apices in observed latent state by ferent endogenous cytokinins (CKs), or as a (1986) after root pruning. Owens et al. their metabolism, change markedly at floral transition; sometimes only for a short period. Depending upon the species, the Ethylene level may increase or decrease. Also, CKs are considered to be very important for must also be considered. Finally, ethylene sexual differentiation (Durand and Durand, Yamamoto et al. (1987) demonstrated that 1984). Thus quantitative as well as quali- flooding greatly increased the production tative variations must be analyzed. of 1-amino-cyclopropane-1-carboxylic acid Curiously, little attention has been paid to (ACC) in the roots and ethylene in the CKs in relationship to flowering of conifers shoots of Pinus halepensis. In a recent (Ross and Pharis, 1976; Tompsett, 1977) experiment (Mercier, personal communi- and it is only recently that endogenous cation), Douglas fir cuttings were treated CKs have also been considered (Taylor et either by stem girdling or by root flooding al., 1984; Zaerr and Bonnet-Masimbert, at the end of shoot elongation. The level of 1987; Doumas et al., 1986; lmbault et al., ACC and its malonyl form (MACC) in- 1988). Also, it is important to note that the creased rapidly in the shoots just after biosynthesis of GAs may be affected by stem girdling and at the end of the flooding CKs (Coolbaugh, 1984). treatment. Flooding had an especially dra- In an experiment on Douglas fir, cytoki- matic and long lasting effect, since 73 nins were analyzed in shoots 3 and 6 days after treatment the levels of ACC and weeks after the beginning of flooding treat- MACC in the shoots were still much higher ments, GA4/7 injection or both (Pilate, than in the control, however, Mercier (per- 1987; lmbault et al., 1988). Isopentenyla- sonal communication) observed their denine (]P) increased markedly in shoots much lower levels in treated roots. Even if of all treated trees but especially in the directly analyzed, not ethylene an was trees which flowered the following spring. increased production after the treatments This might be interpreted as a reduced may be suspected. metabolism of IP forms into zeatin type. IP Exogenous application of ethrel on may also play a direct role in induction, some Cupressaceae species very strongly since it was demonstrated that after its synergized the GA3 flowering effect but exogenous application female flowering did not induce flowering itself (Bonnet- was stimulated (imbault et al., 1988). Masimbert, 1971When applied to Doug- las fir at the same time as GA4/7, ethrel Abscisic acid had a detrimental effect on flowering com- pared to GA4/7 alone (Bonnet-Masimbert, In the same experiment, Pilate (1987) 1983). This may be a question of improper observed an increase of abscisic acid timing, since treating Norway spruce with (ABA) in treated trees compared to ethrel alone doubled the number of female controls, 3 weeks after treatment. This (Remrod, 1976). cones indicates that stress may accompany all the treatments, including the GA4/7 injec- tion. Still, there seems to be no apparent of flower initiation Timing relationship between ABA content and flowering Axillary apices were response. The proper timing of treatment application observed, but this increase in ABA not is crucial to successful flower induction for may retard maintain the development or
temperate conifers (Owens and problem is to find a biochemical marker some Blake, 1985). But whether the differentia- that is specific to the transition stage and, tion is if possible, at the level of the shoot instead period previously as narrow as was thought is questionable. Most treat- of the meristem. Certainly, protein analysis now ments are still applied as if initiation were using the molecular biology tools could a biological feature strictly related to, e.g., help, but so far it has not yet been done vegetative bud phenology or different on flowering in conifers. phases of shoot elongation (Ross, 1983). Recent studies in Douglas fir (Daoudi, This often improves the response to treat- 1988) indicated that some amines, like ments with GAs. But is this relationship putrescine and tyramine, either free or in still true when cultural treatments are conjugated forms, might play such a role. added to GAs? In Douglas fir, where initia- In fact, during the rest period, when sexual tion takes place normally in the spring buds were already differentiated, the ratio around bud-burst (Owens, 1969), root of free putrescine to free tyramine was pruning postponed initiation to the end of 2-3 times higher in vegetative shoots than the growth period (Owens et al., 1986). in shoots bearing male or female buds. Under natural conditions, initiation can Also, male bearing shoots had more neu- even be obtained on lammas shoots (Bon- tral conjugates of putrescine in contrast to net-Masimbert and Lanares, 1978). In this female bearing shoots which had more case, the effect of severe summer water basic ones. A similar distribution was stress seemed to have initiated cone observed in tobacco (Cabanne et al., induction after meristematic activity 1977). resumed due to heavy rains in late sum- These biochemical of changes early mer, completely independently of the stages of initiation have yet to be verified photoperiod. in conifers.Certainly in some herbaceous plants (Cabanne et ai., 1977; Martin-Tan- guy et al., 197t3, 1984) hydroxycinnamic acid amides not only gave an early indica- Possible biochemical markers tion of lowering initiation, but also they able to stimulate when flowering were applied exogenously. In apple trees, the Proper timing of treatments must be fur- exogenous application of putrescine, sper- ther redefined and knowledge of specific midine or spermine significantly increased biochemical markers that are readily iden- the floral development (Rohozinski et al., tifiable and sensitive at the earliest stages 1986). Polyamines and ethylene syn- of flower induction are required. Specific theses interfered strongly with each other techniques, such as immunocytochemical (Slocum et al., 1984) and also interacted assays, have been applied at the meriste- with other PGRs, especially GAs (Dai et matic level on some herbaceous angio- al., 1982) and CIKs (Cho, 1983). sperms. However, within trees, only a Finally, these polyamines also have a small proportion of meristems will actually close relationship with ammoniacal nitro- be converted into sexual buds. Even for gen nutrition through arginine metabolism. shoots within the zone of sexual activity, In apple trees, ammoniacal fertilization large between-shoot variation is observed. only affects flowering after cessation of This complex crown architecture of trees shoot elongation, whereas polyamines makes the sampling problem for biochemi- seem to have an effect independent of cal studies on the early steps of flowering growth status (Rohozinski et al., 1986). a crucial one. Another approach to this
GAs. Finally, much more has to be known Previous studies on Pinus eliotii (Barnes on the effect of climatic conditions, i.e., and Bengtson, 1968) clearly showed that the major effect of NH fertilization in supply, temperature, light intensity, water 3 4 O April and June primarily affects the argi- which make the tree able to respond or nine content (increases of 140% for argi- not to the so-called inductive treatments (Philipson, 1983). In view of the deve- nine compared with only 15% for total loping indoor containerized orchards, this nitrogen). Significant, positive correlations exist between free arginine content and will certainly be an important key to flow- fertilization and between female flowering ering success. and fertilization. Important clonal varia- tions are observed. On the other hand, direct injection of arginine into branches of Acknowledgments Douglas fir from the end of April to the end of June did not stimulate flowering (McMullan, 1980). It seems therefore that The author is grateful to Dr. J.W. Webber for fruitful discussions and for his kind help in polyamines have to be studied further in improving the English version of this paper. relationship to vegetative growth and floral possible biochemical development as markers well active components of as as flowering. References Barnes R.L. & Bengtson G.V. (1968) Effect of fertilization, irrigation, and cover cropping on Conclusion flowering and on nitrogen and soluble sugar composition of slash pine. For. Sci. 14, 172-180 Bonnet-Masimbert M. (1971) Induction flora- From the few examples presented in this précoce chez Cupressus arizonica et le review, it is clear that all the factors af- Chamaecyparis lawsoniana. Silvae Genet. 20, 82-90 fecting flowering, whether they envi- are Bonnet-Masimbert M. (1982) Influence de 1’6tat ronmental, cultural biochemical, interact or d’activit6 des racines sur la floraison induite par extensively and that it is no longer pos- des gibb6rellines 4 et 7 chez Pseudotsuga sible to consider them separately. Certain- menziesii (Mirb.) Franco. Silvae Genet. 31, 178- ly for conifers, GAs are major components 182 in this process, but their biosynthesis and Bonnet-Masimbert M. (1983) Stimulation de la the interaction with biosynthetic pathways floraison chez les conifbres: perspectives offertes par l’utilisation des r6gulateurs de crois- to other PGRs need to be more fully sance. Coll. COLUMA: Les substances de understood. There is one limit to the anal- croissance et leur utilisation en agriculture, of endogenous PGRs, regardless of ysis ACTA, Paris, 2, 480-486 the methodology used (i.e., bioassay or Bonnet-Masimbert M. (1987) Floral induction in immunological methods): it is always very conifers: a review of available techniques. For. Ecol, Manage. 19, 135-146 time consuming. This limits the number of samples which can be analyzed, especial- Bonnet-Masimbert M. & Lanares R. (1978) Induction florale sur pousses d’ao0t chez le ly since it is now clear that large numbers Douglas (Pseudotsuga menziesii). Can. J. For. of analyses are necessary for precise Res. 8, 247-252 kinetic studies. Emphasis has to be given Bonnet-Masimbert M. & Zaerr J.B. (1987) Hor- to the development of well-adapted quick monal control of tree growth. 2. The role of and precise methodologies for PGR anal- plant growth regulators in promotion of flow- ering. Plant Growth Regul. 6, 13-35 yses, especially the very difficult group of
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