Two‐tier morpho‐chemical defence tactic inAethionemavia fruit morph plasticity and glucosinolates allocation in diaspores

Abstract

Fruit dimorphism and the production of glucosinolates (GSLs) are two specific life history traits found in the members of Brassicales, which aid to optimize seed dispersal and defence against antagonists, respectively. We hypothesized that the bipartite dispersal strategy demands a tight control over the production of fruit morphs with expectedly differential allocation of defensive anticipins (GSLs). In dimorphic Aethionema, herbivory by Plutella xylostella at a young stage triggered the production of more dehiscent (seeds released from fruit) than indehiscent fruit morphs (seeds enclosed within persistent pericarp) on the same plant upon maturity. Total GSL concentrations were highest in the mature seeds of dehiscent fruits from Aethionema arabicum and Aethionema saxatile among the different ontogenetic stages of the diaspores. Multivariate analyses of GSL profiles indicated significantly higher concentrations of specific indole GSLs in the diaspores, which require optimal defence after dispersal (i.e., seeds of dehiscent and fruit/pericarp of indehiscent fruit). Bioassays with a potentially coinhabitant fungus, Aspergillus quadrilineatus, support the distinct defensive potential of the diaspores corresponding to their GSL allocation. These findings indicate a two‐tier morpho‐chemical defence tactic of Aethionema via better protected fruit morphs and strategic provision of GSLs that optimize protection to the progeny for survival in nature.

Morphologically and physiologically diverse fruits of two Lepidium species differ in allocation of glucosinolates into immature and mature seed and pericarp

“…Our results support the hypothesis that the immature pericarp in both fruit types (dehiscent and indehiscent) acts as a source of all GSLs and produces a comparable high level of GSLs, which are translocated to the seeds upon maturation [ 7 ]. Similarly, an increase in the accumulation of 35 S-labelled GSLs in the seeds of Brassica napus is correlated with a decrease in labelled GSLs in the pericarp [ 34 ].…”

“…Indeed, plant defence compounds are not equally distributed within a plant but qualitatively and quantitatively differ between tissues and in addition also with ontogenetic stage [7,8]. Defensive natural products are expected to be optimally distributed to protect tissues with high fitness values and a higher likelihood of being attacked with priority [9,10], as proposed by the optimal defence theory [11].…”

“…The highest concentrations of GLSs can be found in reproductive parts such as flowers and seeds [ 17 ]. A recent study revealed the allocation of different GSLs within seeds and pericarps of dehiscent and indehiscent fruits of Aethionema species (Brassicaceae) [ 7 ]. In these species, seeds accumulated higher GLS concentrations when ripe and particularly indole GLSs differed in their distribution between seed and pericarp depending on the fruit morph.…”

Naturally-primed life strategy plasticity of dimorphic Aethionema arabicum facilitates optimal habitat colonization

“…Such a combination has also been observed in other species and interpreted as a way to overcome high sibling competition in local populations 14,32 . The dimorphism displayed dynamic flexibility in the production of reproductive parts 33 and in the proportion of two fruit morphs (DEH: IND) produced on the same plant in response to temperature 29 , branch removal 33,34 , mechanical damage, and herbivory 35 . This distinct dimorphism of Ae.…”

Fracture of the dimorphic fruits ofAethionema arabicum(Brassicaceae)

“…However, a number of species exhibit fruit and seed heteromorphism (heterodiaspory), where a given trait exhibits a clear bimodal (dimorphism) or multimodal (heteromorphism) distribution (Imbert 2002;. Such intra-individual variation can often occur within the same fruiting head (infructescence) and be associated with distinct morphophysiological properties Lenser et al 2016;Liu et al 2018;Bhattacharya et al 2019). The phenomenon of heterodiaspory is of particular importance for relatively short-lived species in spatio-temporally unpredictable environments, and may function as a bethedging survival strategy (Venable 1985), particularly in species distributed in desert, saline, and other frequently-disturbed habitats (Imbert 2002;.…”