Germination Dimorphism in Suaeda acuminata: A New Combination of Dormancy Types for Heteromorphic Seeds

Phenomenon of seeds heteromorphic is found in more than 200 species, and they usually differ in color, size and shape, as well as in dispersal capacity and germination requirements. Desert plants may develop various germination strategies that are adaptations to extreme environments. In the past, many papers reported differential germination of heteromorphic seeds, but few studies defined the dormancy class, level and type in the seeds.

Suaeda acuminata is a desert herb restricted to central Asia. In China, S. acuminata is found only in the inland saline-alkaline deserts in Xinjiang. S. acuminata can produce two morphologically distinct types of seeds on the same plant: brown with soft coarse seed coat and black with rigid smooth seed coat. Seed heteromorphism provides researchers with an optimal opportunity to study different dormancy types and dormancy-breaking mechanisms of the same plant species.

Therefore, prof. TIAN Changyan and his research team used the S. acuminate as an example to compare germination characteristics of the dimorphic seeds, ascertain their dormancy types and give the hormonal explanation. The two seed types of S. acuminata absorbed water at different rates with brown seeds imbibing water faster. Germination percentages of brown seeds were significantly higher than those of black seeds in all temperature and light regimes tested. Eight weeks of cold stratification did not break dormancy of black seeds, whereas exogenous gibberellic acid (GA3) promoted germination. Excised embryos of untreated black seeds produced normal seedlings. Contents of zeatin riboside (ZR), GA3 and abscisic acid (ABA) of brown seeds were significantly higher than that of black seeds; while contents of indole-3-acetic acid (IAA) of black seeds were significantly higher than that of brown seeds. Brown seeds of S. acuminata are non-dormant, whereas black seeds have intermediate physiological dormancy (PD). Interaction among ZR, ABA and GA3 may play an important role in dormancy status of both seed types. This is the first report of nondormancy and intermediate PD in a heteromorphic species.

The main findings of this study have been published on South African Journal of Botany, 2012, 78: 270-275 (http://www.sciencedirect.com/science/article/pii/S0254629911000822).