Light as environmental regulator for germination and macrocotyledon development in Streptocarpus rexii (Gesneriaceae)

We report on the effects of exogenously applied hormones on the lateral and apical dominance that governs morphogenesis in the unifoliate Streptocarpus wendlandii. In this phenotype, lateral dominance is extreme as the plants only retain a macrocotyledon that develops into a leaf-like phyllomorph by means of a basal meristem and do not show apical growth. Gibberellin applications suppressed the basal meristem activity of the macrocotyledon resulting in an isocotylous seedling with two microcotyledons and caused the formation of a primary phyllomorph, which suggests that the groove meristem, a shoot apical meristem equivalent, is released from apical suppression by the basal meristem. Interestingly, uniconazol, a gibberellin biosynthesis inhibitor, also caused a reduction in basal meristem activity, but without primary phyllomorph formation, suggesting that some gibberellin is required for proper function of the basal meristem. Co-application of gibberellin and cytokinin resulted in two macrocotyl...

https://www.tandfonline.com/doi/pdf/10.1080/0028825X.2012.671775

Gibberellin as a suppressor of lateral dominance and inducer of apical growth in the unifoliate Streptocarpus wendlandii (Gesneriaceae)

An overview is given of the current knowledge of the genetic and physiological mechanisms underlying the morphological diversity exhibited by Gesneriaceae plants, one of the larger angiosperm families with more than 3200 species. The development of vegetative structures is highly diversified and includes several unusual features, such as anisocotyly, observed in some genera such as Streptocarpus or Monophyllaea, where one cotyledon develops continuously after germination to form phyllomorphs, rather than leaves. Some anisocotylous plants retain only the continuously developing macrocotyledon as photosynthetic tissue to form ‘one-leaf plants’. Recent Evo-Devo studies have shed some light on the origin and behavior of meristems in such phyllomorphic plants. The plant hormone, cytokinin and environmental factors, such as light, are likely to be the key players in this scenario. Reversions to vegetative development of floral meristems are observed in the genus Titanotrichum. Here, the flower meristems change to form bulbils at the end of the flowering season, a means of asexual mass reproduction. Both phenomena, anisocotyly and bulbil meristem formation are interesting cases of the diversification of meristem behavior in plants, which may be responsible for the generation of such high levels of phenovariation observed in Gesneriaceae.

T. Nagata

Papers

High morphological plasticity in Gesneriaceae meristems: reversions in vegetative and floral development.