Maturation in Larch

Abstract

The effect of maturation on the morphological and photosynthetic characteristics, as well as the expression of two genes involved in photosynthesis in the developing, current year foliage of Eastern larch (Larix laricina [Du Roi]) is described. These effects were observed on foliage during the third growing season after grafting of scions from trees of different ages onto 2 year old rootstock. Specific leaf weight (gram dry weight per square meter), leaf cross-sectional area (per square millimeter), and chlorophyll content (milligram per gram dry weight) all increase with increasing age in long shoot foliage from both indoor-and outdoor-grown trees. Net photosynthesis (NPS) (mole of CO2 per square millimeter per second) increases with age on indoor-but not outdoor-grown trees. NPS also increases with increased chlorophyll content, but outdoor-grown scions of all ages had higher chlorophyll content, and chlorophyll does not appear to be limiting for NPS outdoors. To extend these studies of maturationrelated differences in foliar morphology and physiology to the molecular genetic level, sequences were cloned from the cab and rbcS gene families of larch. Both cab and rbcS gene families are expressed in foliage but not in roots, and they are expressed in light-grown seedlings of larch but only at very low levels in dark-grown seedlings (-2% of light-grown seedlings). Steadystate cab mRNA levels are relatively higher (-40%) in newly expanding short shoot foliage from juvenile plants compared to mature plants. Unlike cab, the expression of the rbcS gene family did not seem to vary with age. These data show that the maturation-related changes in morphological and physiological phenotypes are associated with changes in gene expression.

Growth responses of branch cuttings of Cordia africana to physiological age

“…This trend is consistent with the sigmoidal pattern of tree growth, which stipulates that growth generally increases to a peak after initiation and declines with further increase in tree age (Weiner, 2001;Bond et al, 2007). The results also emphasize the fact that a new independent plant produced by vegetative propagation is a clone, which can express morphological phenotypes of the donor tree (Hutchinson et al, 1990;Ritchie and Keeley, 1994;Hartmann et al, 2002). The findings on C. africana reported here are in accordance with those of several other studies.…”

“…This means that physiological processes that control growth are likely genetically regulated and should show direct age-mediated changes in trees. Hutchinson et al (1990) explored the role of gene expression in the photosynthesis of grafted scions from L. laricina trees of different ages. The cab genes that encode elements of the photosynthetic apparatus were found to be expressed at lower levels in mature than young plants.…”

“…The effects of age can be decoupled from those of size by using rooted cuttings or grafted scions taken from different aged ortets, to produce trees of uniform size, but with shoots of different physiological ages (Browne et al, 1997;Krakowsky et al, 2005). The basis of these approaches is that maturation-related properties of trees are associated with changes in gene expression (You et al, 2014), and can, therefore, be inherited by vegetative propagules (Greenwood et al, 1989;Hutchinson et al, 1990). Most of the work on maturation has been descriptive, and comprehensive experimental studies on woody species are rare.…”

The Past, Present, and Future of Vegetative Phase Change

“…In maize, the propensity of adult shoots to undergo rejuvenation in culture has facilitated the identification of genes involved in vegetative phase change (Strable et al, 2008). A few phase-specific genes have also been identified in larch (Larix laricina; Hutchinson et al, 1990) and English ivy (Hedera helix; Woo et al, 1994). However, there is still no comprehensive picture of the changes in gene expression that occur during vegetative growth in any plant species.…”

Transcriptome analysis provides insights into wood formation during larch tree aging

“…In studies of the molecular mechanisms of tree aging, many age-related genes have been identified (Busov et al 2004;Carlsbecker et al 2004;Diego et al 2004;Fernández-Ocaña et al 2010;García-López et al 2014;Hutchison et al 1990;Li et al 2010Xu et al 2016;Zhang et al 2016), such as miR156 (Wang et al 2011b) and Flowering Locus T (Böhlenius et al 2006;Hsu et al 2006Hsu et al , 2011, and some have been used to change the agronomic traits of plants (Flachowsky et al 2012;Kotoda et al 2006;Li et al 2013a;Yamagishi et al 2014). Larix kaempferi is a forest tree of important ecological and economic value, widely grown in the Northern Hemisphere, but its genome has not been sequenced.…”