Abstract
The morphology and physiology of diaspores play crucial roles in determining the fate of seeds in unpredictable habitats. In some genera of the Brassicaceae different types of diaspores can be found. Lepidium appelianum produces non-dormant seeds within indehiscent fruits while in L. campestre dormant seeds are released from dehiscent fruits. We investigated whether the allocation of relevant defence compounds into different tissues in different Lepidium species may be related to the diverse dispersal strategy (indehiscent and dehiscent) and seed physiology (non-dormant and dormant). Total glucosinolate concentration and composition were analysed in immature and mature seeds and pericarps of L. appelianum and L. campestre using high-performance liquid chromatography. Moreover, for comparison, transgenic RNAi L. campestre lines were used that produce indehiscent fruits due to silencing of LcINDEHISCENCE, the INDEHISCENCE ortholog of L. campestre. Total glucosinolate concentrations were lower in immature compared to mature seeds in all studied Lepidium species and transgenic lines. In contrast, indehiscent fruits of L. appelianum maintained their total glucosinolate concentration in mature pericarps compared to immature ones, while in dehiscent L. campestre and in indehiscent RNAi-LcIND L. campestre a significant decrease in total glucosinolate concentrations from immature to mature pericarps could be detected. Indole glucosinolates were detected in lower abundance than the other glucosinolate classes (aliphatic and aromatic). Relatively high concentrations of 4-methoxyindol-3-ylmethyl glucosinolate were found in mature seeds of L. appelianum compared to other tissues, while no indole glucosinolates were detected in mature diaspores of L. campestre. The diaspores of the latter species may rather depend on aliphatic and aromatic glucosinolates for long-term protection. The allocation patterns of glucosinolates correlate with the morpho-physiologically distinct fruits of L. appelianum and L. campestre and may be explained by the distinct dispersal strategies and the dormancy status of both species.
Highlights
For seed plants, fruit structures and corresponding dispersal strategies are life history traits of particular importance influencing plant fitness
We aimed to investigate whether the differences in dispersal strategy and seed dormancy status between the two Lepidium species correspond to the allocation of total and individual GSLs in immature and mature seeds and pericarps
Seeds of the transgenic Lepidium campestre line RNAiINDa, in which silencing of LcINDEHISCENT by RNAi is established, resulting in indehiscent fruits, were collected from plants cultivated at Friedrich Schiller University Jena; for details of cloning, transformation and plant cultivation procedures, see [24])
Summary
Fruit structures and corresponding dispersal strategies are life history traits of particular importance influencing plant fitness. Dehiscent fruits are the most common fruit morph among the Brassicaceae and are assumed to be the ancestral diaspore morph in this family [3]. These fruits open along a predetermined dehiscence zone at the pericarp upon maturity and release their seeds [4]. In indehiscent fruits the pericarp envelopes the seeds even after dispersal, until it decomposes and only releases the seeds. Both fruit types are associated with different dispersal strategies, i.e., dehiscent fruits may escape unfavourable conditions via long-distance dispersal [5], while indehiscent fruits may escape in time by fractional or delayed germination [6]. In indehiscent fruits, the pericarp needs to be provided with a higher defence than the enclosed seeds
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