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Phase change-related variations of dome shape in Eucalyptus urophylla X Eucalyptus grandis shoot apical meristems

Mankessi F., Saya A.R., Boudon F., Guédon Y., Montes F., Lartaud M., Verdeil J.L., Monteuuis O.. 2010. Trees, 24 (4) : p. 743-752.

DOI: 10.1007/s00468-010-0444-7

Shoot apical meristem (SAM) domes derived from five different outdoor and in vitro sources of juvenile and mature Eucalyptus urophylla 9 Eucalyptus grandis akin genotypes were compared. Overall measurements of SAM dome height H and diameter D ranged from 2 to 35 lm and 20 to 80 lm, with significant differences according to the various physiological origins of plant material investigated. SAM domes from the mature trees ''Mat'' were taller than those from the rejuvenated ministock plants ''Rej''; from the in vitro microcuttings ''IVM'' of the same clone and also from the in vitro juvenile seedlings ''IVJ'', whereas outdoor seedlings ''Juv'' exhibited intermediate SAM dome height. SAM domes from the rejuvenated material ''Rej'', from the in vitro mature ''IVM'' and juvenile ''IVJ'' origins were also narrower than those from the outdoor seedlings ''Juv'' and to lesser extent than those from the mature trees ''Mat''. Overall, the mature source ''Mat'' displayed bigger and somehow sharper hemispherical domes than those from ''Rej'' and ''Juv'', physiologically more juvenile, or those from the in vitro origins ''IVM'' and ''IVJ'' which looked flatter and smaller. SAM dome height, diameter D and H/D values varied also significantly according to the plastochron. More specifically, H, D, and H/D SAM differences between the five origins were not significant during the early plastochron phase corresponding to leaf initiation, to become more salient as leaf structures started to elongate and to differentiate. This was particularly obvious for mature tree ''Mat'' SAM dome shapes which showed at this stage much higher H/D values than the other SAM sources. A shape index S used for characterizing more accurately dome shape confirmed these trends. These observations provide additional arguments to the view that juvenility in trees becomes more and more time- and shoot-tip restricted as ageing increases in the course of time during the ontogenetical process and could be ultimately confined to the most organogenic phase of SAM, from which shoot characteristics derive.

Mots-clés : eucalyptus urophylla; eucalyptus grandis; congo

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