Microspore-derived embryogenesis in Capsicum annuum: subcellular rearrangements through development

14 páginas, 7 figuras -- PAGS nros. 709-722Background information. In vitro-cultured microspores, after an appropriate stress treatment, can switch towards an embryogenic pathway. This process, known as microspore embryogenesis, is an important tool in plant breeding. Basic studies on this process in economically interesting crops, especially in recalcitrant plants, are very limited and the sequence of events is poorly understood. In situ studies are very convenient for an appropriate dissection of microspore embryogenesis, a process in which a mixture of different cell populations (induced and non-induced) develop asynchronically. Results. In the present study, the occurrence of defined subcellular rearrangements has been investigated during early microspore embryogenesis in pepper, an horticultural crop of agronomic interest, in relation to proliferation and differentiation events. Haploid plants of Capsicum annuum L. (var. Yolo Wonder B) have been regenerated from in vitro anther cultures by a heat treatment at 35°C for 8 days. Morphogenesis of microspore-derived embryos has been analysed, at both light and electron microscopy levels, using low-temperature-processed, well-preserved specimens. The comparison with the normal gametophytic development revealed changes in cell organization after embryogenesis induction, and permitted the characterization of the time sequence of a set of structural events, not previously defined in pepper, related to the activation of proliferative activity and differentiation. These changes mainly affected the plastids, the vacuolar compartment, the cell wall and the nucleus. Further differentiation processes mimicked that of the zygotic development. Conclusions. The reported changes can be considered as markers of the microspore embryogenesis. They have increased the understanding of the mechanisms controlling the switch and progression of the microspore embryogenesis, which could help to improve its efficiency and to direct strategies, especially in agronomically interesting cropsThis work was supported by grants from the Spanish MCyT (BOS2002-03572) and Comunidad de Madrid (CM 07G/0026/2003Peer reviewe

The switch of the microspore developmental program in Capsicum involves HSP70 expression and leads to the production of haploid plants

The switch of the gametophytic developmental program of the microspore towards embryogenesis to form a haploid plant represents an important tool in plant breeding for obtaining isogenic lines and new varieties through double-haploid plants. This process can be induced in microspore in vitro cultures by stress treatments, like starvation or heat-shock. Microspore embryogenesis also constitutes an interesting in vitro system for basic studies on cellular and molecular mechanisms controlling plant development, cell fate, stress response and signalling pathways. This process has been induced in many plant species but little is known about the mechanisms and factors involved in this change of developmental program. In this work, various ultrastructural in situ approaches have been performed to characterize changes in the subcellular organization and the localization of stress proteins, specifically the HSP70, during the induction and early microspore embryogenesis