Pinpointing the timing of meiosis: a critical factor in evaluating the impact of abiotic stresses on the fertility of cereal crops.

The development of male gametes, vital to sexual reproduction in crops, requires meiosis followed by successive mitotic cell divisions of haploid cells. The formation of viable pollen is especially vulnerable to abiotic stress, with consequences both for yield and for grain quality. An understanding of key molecular responses when specific stages during pollen development are subjected to stress (e.g. heat) is possible only when sampling is carefully informed by developmental biology. Traditionally, morphological characteristics have been commonly used in cereals as 'indicators' of male reproductive stages. We argue that these morphological attributes are strongly influenced by genotype and genotype-environment interactions and cannot be used reliably to define developmental events during microsporogenesis and microgametogenesis. Furthermore, asynchronous development along the axis of a single inflorescence calls for selective sampling of individual florets to define specific reproductive stages accurately. We therefore propose guidelines to standardise the sampling of cells during male reproductive development, particularly when interrogating the impact of stress on susceptible meiosis. Improved knowledge of development will largely negate the variability imposed by genotype, environment and asynchronous development of florets. Highlighting the subtleties required for sampling and investigation of male reproductive stages will make the selection of abiotic stress-tolerant cereal genotypes more reliable.