Heat Stress Effects on Flowering and Reproduction in Linum usitatissimum (Flax)

Abstract

ABSTRACT Heat stress can detrimentally affect the reproductive capacity of many plants. The effect of a one or two week heat stress (HS) on flowering, seed set, pollen viability and germinability of Linum usitatissimum (flax) was monitored. Flower formation in flax was not affected by the HS however, boll formation and seed set were reduced after two to three days of HS. When the HS was removed the stressed plants showed a compensatory response whereby they continued to flower and set seed until the total production of both was equivalent to that of the control plants. However, HS significantly prolonged the duration of flowering. The weight per boll and per seed was reduced by HS and the number of malformed, sterile seeds increased with the duration of the it. Pollen viability was not affected by HS until the sixth day of high temperature. By the tenth day of HS pollen appeared misshapen. Pollen germinability was decreased by the sixth day of HS and by the tenth day no pollen was seen to germinate. However, these late effects on pollen cannot account for the early decrease in boll formation observed in the heat stressed plants. To try and improve flower thermotolerance by modifying the HS response in the pollen and the ovaries, the expression patterns of two Arabidopsis thaliana promoters in flax were examined. The expression of AGAMOUS (AG) promoter was expressed primarily in the reproductive structures, notably in pollen, but not in the ovules of flax. Thus, the AG promoter may be a good choice to help improve the thermotolerance of male reproductive structures in flax. Secondly, the expression of the A. thaliana HSP101B promoter in flax was examined through the use of a HSP101B::GUS fusion construct. HSP101B-directed GUS expression was observed in leaves where expression was constitutive, HS induced, wound induced or combinations of the above. These data suggest that the regulatory elements of this promoter have been conserved between flax and A. thaliana. The expression pattern of HSP101B was observed in heat stressed flowers. HS flax pollen was able to strongly express HSP101B directed GUS. In seedlings, the HSP101B promoter was also found to be active in response to a variety of stresses. HSP101B appears to be important in many different stress responses in flax and may be a good choice as a promoter to help improve flower thermotolerance.