Seed heteromorphism, an adaptive trait of desert plant species

Seed heteromorphism provides plants with alternative strategies for survival in unfavourable environments. Seed heteromorphism is a phenomenon in which an individual plant produces two or more distinct types of seeds and has commonly been observed in semi-arid, saline and other harsh environments. Heteromorphic seeds of individual plants have been seen to differ in colour, shape, size, mechanism of seed dispersal and dormancy length. Suaeda aralocaspica is an annual halophyte native to the deserts of central Asia with succulent leaves that grows in saline–alkaline sandy soil. Previous studies have reported the species to produce two distinct seed morphs, that differ in colour (brown or black) and have differences in dormancy characteristic and salt tolerance. However, little is known about the effects of the genetic and environmental factors or their interaction on seed heteromorphism and its variations.

In their new study published in AoBP, Cao et al. study seed morphology, differentiation of morphs and fruit-setting patterns in Suaeda aralocaspica using seeds collected from natural populations in the cold desert of the Junggar Basin in Xinjiang province, China. Contrary to previous reports of this species producing only two seed morphs, they classified a third type of seed morph. They report the production of brown, large black and small black seeds displaying differences in colour, size, mass and germination behaviour. The large and small black seeds were distinguished by their origin from female or bisexual flowers, respectively. They also reveal that the formation and variations of seed heteromorphism in S. aralocaspica are caused by a combination of genetic aspects (seed positioning, seed coat differentiation, gene expression, etc.) and environmental factors (annual precipitation, temperature, illumination, etc.).  Their findings contribute to the understanding of seed heteromorphism as a potential adaptive trait of desert plant species.