College of Life Sciences, Wuhan University, Wuhan, China.
BMC Plant Biol. 2010 May 20;10:91. doi: 10.1186/1471-2229-10-91.
Floral traits within plants can vary with flower position or flowering time. Within an inflorescence, sexual allocation of early produced basal flowers is often female-biased while later produced distal flowers are male-biased. Such temporal adjustment of floral resource has been considered one of the potential advantages of modularity (regarding a flower as a module) in hermaphrodites. However, flowers are under constraints of independent evolution of a given trait. To understand flower diversification within inflorescences, here we examine variation and covariation in floral traits within racemes at the individual and the maternal family level respectively in an alpine herb Aconitum gymnandrum (Ranunculaceae).
We found that floral traits varied significantly with flower position and among families, and position effects were family-specific. Most of the variance of floral traits was among individuals rather than among flowers within individuals or among families. Significant phenotypic correlations between traits were not affected by position, indicating trait integration under shared developmental regulation. In contrast, positive family-mean correlations in floral traits declined gradually from basal to distal flowers (nine significant correlations among floral traits in basal flowers and only three in distal flowers), showing position-specificity. Therefore, the pattern and magnitude of genetic correlations decreased with flower position.
This finding on covariation pattern in floral reproductive structures within racemes has not been revealed before, providing insights into temporal variation and position effects in floral traits within plants and the potential advantages of modularity in hermaphrodites.
植物的花部特征可能随花位或花期而变化。在花序中，早产生的基部花的性分配通常偏向雌性，而晚产生的远端花则偏向雄性。这种花部资源的时间调整被认为是雌雄同体中模块性（将花视为一个模块）的潜在优势之一。然而，花部特征的独立进化受到限制。为了理解花序内花部的多样化，我们分别在个体和母系家族水平上，在高山草本植物 Aconitum gymnandrum（毛茛科）的总状花序内，研究花部特征的变异和协同变化。
我们发现花部特征随花位和家族而异，并且位置效应具有家族特异性。大多数花部特征的变异是在个体之间，而不是在个体内的花朵之间或家族之间。特征之间的显著表型相关性不受位置影响，表明在共同发育调控下特征的整合。相比之下，花部特征的正家族均值相关性从基部到远端花朵逐渐下降（基部花朵的 9 个显著相关特征，而远端花朵只有 3 个），表现出位置特异性。因此，遗传相关性的模式和幅度随花位而降低。
这一关于总状花序内花部生殖结构协同变化模式的发现以前没有揭示过，为植物内花部特征的时间变化和位置效应以及雌雄同体中模块性的潜在优势提供了新的认识。
