Annals of Botany

Male function fails when the heat is on

The consequences of global warming for yields of individual crop species are difficult to predict. Moderate increases in temperature affect different plant processes in different ways; further, those responses will differ between species. Thus, studies of individual species, such as the work on tomato (Lycopersicon esculentum) by Sato et al., Chiba and Osaka, Japan (pp. 731–738) are important in our understanding of the effects of climate change. The authors grew plants under control conditions (28/22 °C) or at moderately increased temperatures (32/26 °C), the increase representing what is expected, according to some models, by about 2075. The first key finding was that general features of growth, including the number of flowers produced, were not affected by the temperature increase. However, the number of fruit set at the higher temperature was only 25 % of that under control conditions. This reduction was entirely ascribable to a failure of male function. Stamens were shorter than in control plants and although they produced normal amounts of pollen, the number of pollen grains released was very markedly reduced while pollen viability dropped from approx. 85 % to approx. 20 %. There were also marked changes in anther biochemistry. At the higher temperatures, sucrose accumulated at the expense of reducing sugars; this being correlated with a reduction in the amount of mRNA encoding acid invertase (although this may not be the sole enzyme regulating sucrose hydrolysis). There was also an increased accumulation of proline at the meiosis stage of pollen development. The authors ascribe pollen failure to poor transport of proline from the tapetum to the developing pollen, a suggestion supported by the decrease in the amount of mRNA encoding proline transporters. Indeed, the authors focus on the idea that a delay in tapetal breakdown, and therefore a delay in transferring nutrients to the developing pollen, may hold the key to male dysfunction at the warmer temperatures.