Park Eung-Jun, Lee Wi-Young, Kurepin Leonid V, Zhang Ruichuan, Janzen Loeke, Pharis Richard P
Department of Forest Genetic Resources, Korea Forest Research Institute, Suwon 441-847, Republic of Korea.
Biological Sciences Department, University of Calgary, Calgary, Alberta, Canada T2N 1N4 Present address: Department of Biology, Western University, London, Ontario, Canada N6A 5B7.
Tree Physiol. 2015 Jan;35(1):86-94. doi: 10.1093/treephys/tpu102. Epub 2014 Dec 22.
In an even-aged pine forest trees can vary considerably in stem size. We examined the basis for this anomaly using a retrospective approach. Twelve open-pollinated families of Pinus densiflora Sieb. et Zucc. were deliberately chosen for their variation in stem volumes at age 32 years. Seedlings obtained from these families were grown to age 6 months under optimal nursery conditions. Endogenous levels of growth hormones (auxin [IAA] and gibberellins [GAs]) and expression of the GA biosynthesis gene, PdGA20ox1, all assessed at age 3 months, were significantly correlated, across family, with seedling stem and/or shoot dry biomass at age 6 months. Retrospective comparisons of seedling growth, seedling stem tissue GA(20) and seedling stem expression levels of PdGA20ox1 were then made, across family, with tree stem growth at age 32 years. Age 6 months length and shoot dry biomass at age 6 months showed positive and significant Pearson's correlations with age 32 years tree stem diameters and a tree stem volume index, as did seedling stem tissue GA(20). Even seedling stem PdGA20ox1 expression levels were positively and near significantly (P = 0.088) correlated with age 32 years tree stem diameters. Auxin and GAs control nursery growth of seedlings at the family level, and this control also extends, for GAs at least, to field growth of older trees. We propose that family differences in PdGA20ox1 gene expression, and thus endogenous GA levels, may explain much of the natural variation seen for tree stem size in even-aged pine forests. If our hypothesis is correct, then the heritable components of variation in tree stem growth capacity should be predictable by hormonal and gene expression profiling. Such profiling, combined with the measurement of seedling phenotypic growth characters, could have the potential to accelerate the early selection of those conifer families that possess traits for inherently rapid stem wood growth.
在同龄松树林中，树木的茎干大小可能存在很大差异。我们采用回顾性方法研究了这种异常现象的原因。特意选择了12个日本赤松（Pinus densiflora Sieb. et Zucc.）的开放授粉家系，因其在32岁时茎干体积存在差异。从这些家系获得的幼苗在最佳苗圃条件下生长至6个月龄。在3个月龄时评估的生长激素（生长素[IAA]和赤霉素[GAs]）的内源水平以及GA生物合成基因PdGA20ox1的表达，在各个家系中均与6个月龄时幼苗的茎干和/或地上部干生物量显著相关。然后，在各个家系中对幼苗生长、幼苗茎组织GA(20)以及PdGA20ox1的幼苗茎表达水平与32岁时的树木茎干生长进行了回顾性比较。6个月龄时的长度和6个月龄时的地上部干生物量与32岁时的树木茎干直径和树木茎干体积指数呈显著正相关，幼苗茎组织GA(20)也是如此。甚至幼苗茎PdGA20ox1表达水平与32岁时的树木茎干直径呈正相关且接近显著相关（P = 0.088）。生长素和赤霉素在家庭水平上控制幼苗的苗圃生长，并且这种控制至少对于赤霉素而言，也延伸到了老龄树木的田间生长。我们提出，PdGA20ox1基因表达的家系差异以及由此产生的内源GA水平，可能解释了同龄松树林中树木茎干大小所观察到的大部分自然变异。如果我们的假设正确，那么树木茎干生长能力变异的遗传成分应该可以通过激素和基因表达谱进行预测。这种谱分析与幼苗表型生长特征的测量相结合，有可能加速对那些具有固有快速茎干木材生长特性的针叶树家系的早期选择。
