High temperature stress of Brassica napus during flowering reduces micro- and megagametophyte fertility, induces fruit abortion, and disrupts seed production

Abstract

High temperature stress (HTS), during owering, decreases seed production in many plants. To determine the effect of a moderate HTS on owering, fruit and seed set in Brassica napus, plants were exposed to a HTS (8/16 h dark/light, 18 C night, ramped at 2 C h 1 , over 6 h, to 35 C for 4 h, ramped at 2 C h 1 back to 23 C for 6 h) for 1 or 2 weeks after the initiation of owering. Although owering on the HTStreated plants, during both the 1 week and 2 week HTS treatments, was equal to that of control-grown plants, fruit and seed development, as well as seed weight, were signicantly reduced. Under HTS, owers either developed into seedless, parthenocarpic fruit or aborted on the stem. At the cessation of the HTS, plants compensated for the lack of fruit and seed production by increasing the number of lateral inorescences produced. During the HTS, pollen viability and germinability were slightly reduced. In vitro pollen tube growth at 35 C, from both control pollen and pollen developed under a HTS, appeared abnormal, however, in vivo tube growth to the micropyle appeared normal. Reciprocal pollination of HTS or control pistils with HTS or control pollen indicated that the combined effects of HTS on both micro-and megagametophytes was required to knock out fruit and seed development. Expression proles for a subset of HEAT SHOCK PROTEINs (HSP101, HSP70, HSP17.6) showed that both micro-and megagameto-phytes were thermosensitive despite HTS-induced expression from these genes.