Anther meiosis time is related to winter cold temperatures in apricot (Prunus armeniaca L.)

In temperate woody plants, flowering time is adjusted to the environmental temperature, and survival to cold winter temperatures is achieved through dormancy. But also chilling temperatures during dormancy are required for proper flower bud development and flowering. The time the flower bud remains dormant is both genetically and environmentally controlled, and is a major factor determining the adaptation of species and cultivars to particular ecological conditions because chilling requirements vary greatly among genotypes. Recently this adaptation is jeopardised with climate changing conditions. However, little is known on the biological milestones underpinning these events, and when differences in flowering time are established. In this work we evaluate the hypothesis that anther meiosis time is related to winter cold temperatures, and that differences in flowering time are set up by differences in the time when pollen meiosis occurs. For this purpose, anther development has been characterised in five apricot cultivars with different chilling requirements. The work was done over two years with different weather conditions, a cold and a mild winter. The sporogenous tissues differentiated prior to dormancy and remained in this apparently quiescent stage during the winter. Once chilling requirements were fulfilled, meiosis closely followed and was highly correlated to breaking of endodormancy. Meiosis was completed within one week and was followed by a change in the colour of the anthers from green to yellowish, which could be a useful visual indicator to know that breaking of endodormancy had already occurred. The fact that this sequence of events was consistent in all the cultivars, and different climatic years analysed, supports the hypothesis that winter cold temperatures are related to the time of pollen meiosis, which in turn reflects in different flowering times. (C) 2013 Elsevier B.V. All rights reserved.