Ovary Size in Wheat (Triticum aestivum L.) is Related to Cell Number

Abstract

In wheat and other grain species, variations in kernel size are related to variations in ovary size. It is not known whether environmental factors that are known to affect kernel size may also affect ovary size, thus maintaining the kernel size‐ovary size correlation. Additionally, it is not known whether variations in ovary size in wheat depend on cell size, cell number or both. In this study, ovary size was measured with a stereomicroscope, and ovary wall cell size and number were measured in equatorial cross‐sectional areas of the ovary wall in two common wheat cultivars with different kernel size: Bora (large kernels) and Bologna (small kernels). Plants were grown at low and high N fertilization (0 and 240 kg ha−1) with normal density (450 seeds m−2), and at low and high plant density (200 and 650 plants m−2) with normal fertilization (160 kg N ha−1). The variation in ovary wall size across all data pooled (i.e., including two genotypes, two N and two density treatments, and including within treatment variations), was related to cell number and not to the cell size, which did not vary significantly with cultivar and field practices. With increasing ovule size, ovary wall size increased less than proportionally, thus the ovule/ovary ratio increased. Cell size in the ovary wall showed an upper limit across all treatments, which decreased with increasing cell number. These findings may be useful for breeding programs and field practices aimed at increasing kernel size and yield.

A reductionist approach to dissecting grain weight and yield in wheat

“…Each spikelet will initiate between 8 and 12 floret primordia, although usually just the first four to six florets are potentially fertile and produce a carpel, consisting of the ovary, style and stigma (Kirby and Appleyard ; Evers and Millar ). A strong association has been observed between carpel size and final grain weight, suggesting that grain weight can be determined, maternally, even before grain development per se has started (Calderini et al ; Hasan et al ; Guo et al ; Reale et al ).…”

“…Many of the genes shown to regulate seed size in rice and Arabidopsis appear to act maternally, either pre-or post-fertilization (reviewed by Li and Li 2015). A strong association between carpel size and final grain weight has been documented in wheat (Calderini et al 1999;Calderini and Reynolds 2000;Hasan et al 2011;Xie et al 2015;Reale et al 2017). TaGW2 acts maternally, with 10% increased carpel size in the A-genome knock-out mutant lines compared with wild-type (Simmonds et al 2016).…”

“…The mechanisms by which the carpel and its component tissues influence final grain size are not well understood in wheat and barley. Reale et al () established that the size of both the ovary wall and the ovule itself were associated with larger carpels and grains, largely due to cell number, rather than size. However, the two tissues were not affected to the same extent, resulting in an increased ovule:ovary wall ratio in larger grains.…”

“…However, some genes (e.g. GW2 ) exert their control on grain weight by affecting carpel size, a yield component that is determined during the same growth stages as the definition of grain number (Simmonds et al ; Reale et al ). Hence, for these cases, the interactions between grain number and grain size could be due to competition for resources pre‐anthesis, and not necessarily due to any post‐anthesis events relating to grain filling.…”

Translating auxin responses into ovules, seeds and yield: Insight from Arabidopsis and the cereals

“…Although all angiosperms produce seed, considerable natural variation is present in the timing of reproductive development and size of constituent organs, which impacts the size and number of seeds both among and within related species (Guo et al ; Guo et al ; Li and Yang ). For example, increased ovary size, which is largely due to increased cell number, has been positively linked to the size of mature grains in both wheat and sorghum (Yang et al ; Xie et al ; Reale et al ).…”