Endogenous ABA concentration and cytoplasmic membrane fluidity in microspores of oilseed rape (Brassica napus L.) genotypes differing in responsiveness to androgenesis induction

A better understanding of androgenesis with a focus on the changes in plasma membrane fluidity and endogenous ABA content affecting embryogenesis induction in microspore suspension of B. napus. Changes in plasma membrane fluidity (MF) and ABA content associated with androgenesis induction were under the study. Both parameters were monitored in microspores of two Brassica napus L. genotypes differing in their response to androgenic induction under heat (1 day at 32 A degrees C). MF was assessed by DPH method. ABA content was evaluated by ELISA. Heat caused microspores' plasma membrane to become more rigid. Lower MF in microspores of 'DH 4079' (of high androgenic potential) seems to maintain proper cell protection and leads to efficient embryogenesis induction. Plasma membrane remodelling coincided with changes of ABA content in microspores and in the culture medium in both genotypes. ABA concentration (mu M) and ABA content (fmol per 10(4) microspores or pmol g(-1) FW) were for the first time measured in microspores. ABA concentration (mu M) in microspores and in the culture medium (nM) differed significantly for the genotype and the treatment. The interaction between both variables was also significant. In general, ABA content ranged from < 3.5 to 87.1 fmol per 10(4) microspores. The highest content of ABA was detected in 'DH 4079' microspores at 32 A degrees C. Assuming a mean microspores' radius of 10 mu m, it corresponds to ABA concentration of 2.1 mu M. Heat shock resulted in quantum of medium pH reduction (0.1-0.2) and increased levels of ABA in microspores and in the medium of both tested genotypes. However, heat induced increase of ABA content in microspores of non-responsive 'Campino' had no clear-cut impact, on androgenesis induction efficiency, which suggests a more complex mechanism of process initiation.