Abstract
BackgroundDecreased spikelet fertility is often responsible for reduction in grain yield in rice (Oryza sativa L.). In this study, two varieties with different levels of heat tolerance, Liangyoupeijiu (LYPJ, heat susceptible) and Shanyou63 (SY63, heat tolerant) were subjected to two temperature treatments for 28 days during the panicle initiation stage in temperature/relative humidity-controlled greenhouses: high temperature (HT; 37/27 °C; day/night) and control temperature (CK; 31/27 °C; day/night) to investigate changes in anther development under HT during panicle initiation and their relationship with spikelet fertility.ResultsHT significantly decreased the grain yield of LYPJ by decreasing the number of spikelets per panicle and seed setting percentage. In addition, HT produced minor adverse effects in SY63. The decreased spikelet fertility was primarily attributed to decreased pollen viability and anther dehiscence, as well as poor pollen shedding of the anthers of LYPJ under HT. HT resulted in abnormal anther development (fewer vacuolated microspores, un-degraded tapetum, unevenly distributed Ubisch bodies) and malformation of pollen (obscure outline of the pollen exine with a collapsed bacula, disordered tectum, and no nexine of the pollen walls, uneven sporopollenin deposition on the surface of pollen grains) in LYPJ, which may have lowered pollen viability. Additionally, HT produced a compact knitted anther cuticle structure of the epidermis, an un-degraded septum, a thickened anther wall, unevenly distributed Ubisch bodies, and inhibition of the confluent locule, and these malformed structures may be partially responsible for the decreased anther dehiscence rate and reduced pollen shedding of the anthers in LYPJ. In contrast, the anther wall and pollen development of SY63 were not substantially changed under HT.ConclusionsOur results suggest that disturbed anther walls and pollen development are responsible for the reduced spikelet fertility and grain yield of the tested heat susceptible variety, and noninvasive anthers and pollen formation in response to HT were associated with improved heat tolerance.
Highlights
Decreased spikelet fertility is often responsible for reduction in grain yield in rice (Oryza sativa L.)
The grain yield of LYPJ was reduced by 84% under high temperature (HT) when compared with that under Control temperature (CK), and this change was accompanied by reductions in spikelets per panicle (35%), seed setting percentage (69%), and 1000grain weight (17%)
The anther dehiscence rate was decreased by 5% in LYPJ under HT in comparison with those under CK, and the pollen shedding percentage of the anthers was decreased by 11% (Fig. 1K and L), whereas no significant differences was observed in either trait between CK and HT in SY63
Summary
Decreased spikelet fertility is often responsible for reduction in grain yield in rice (Oryza sativa L.). Decreased pollen viability are tightly associated with abnormal anther development [6,7,8,9] and responsible for spikelet sterility under HT during panicle initiation [3]. The amount of pollen grains on the stigma, in vivo pollen germination on the stigma, and hidden stigmas were positively associated with spikelet fertility under HT at the flowering stage [1, 2, 12,13,14]. These previous reports show that the normal development of reproductive organs is a necessary perquisite for spikelet fertility and grain yield formation under heat stress
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