Increased Ring‐Shaped Chalkiness and Osmotic Adjustment when Growing Rice Grains under Foehn‐Induced Dry Wind Condition

Abstract

Foehn-induced dry wind during grain filling increased ring-shaped chalky kernels in rice {Oryza sativa L.) plants. The objective of this study was to determine physiological mechanisms of the occurrence of ring-shaped chalky kernels. Rice plants were subjected to water deficit in a paddy field after shade by applying dry high-speed wind. Additionally, a growth chamber experiment was conducted with plants in pots to measure the water status under the dry wind condition for 24 h by combining in situ turgor {^'^) assay in developing endosperms with the water potential measurements. The dry (high vapor pressure deficit [VPD]) wind treatment produced the largest number of ring-shaped chalky kernels due to poor starch accumulation, compared with shade or low-VPD wind treatment. The inner endosperm cells, where a high frequency of chalkiness was observed, spatially maintained y by osmotic adjustment before the chalky formation with no decline of grain weight. Dry wind reduced photosynthesis due to a partial stomatal closure after water deficit developed. However, these responses, including those related to the plant water status, returned to a level similar to those of the control plants in a day after the dry wind was stopped. We conclude that (i) H'^ maintenance by osmotic adjustment contributes to grain development under water deficit under foehn conditions and (ii) osmotic adjustment has a role in temporally inhibiting starch accumulation in endosperms, resulting in ring-shaped chalky kernels under foehn-induced water deficit conditions.

Multiple strategies for heat adaptation in rice endosperms revealed by on-site cell-specific analysis

“…During the osmotic adjustment, turgor pressure can be maintained by accumulating osmotically active solutes, such as sugars and amino acids, into the cells (Morgan, 1977; Meyer and Boyer, 1981). As reported previously (Wada et al, 2011; Wada et al, 2014), osmotic adjustment also occurred in the rice endosperms cells growing under dry wind conditions prior to chalky ring formation. On-site cell metabolomics and in situ turgor assay conducted in outer endosperms indicated clear treatment differences in the heat adaptive responses (Figure 3B-E).…”

“…Oryza sativa L. ‘Koshihikari’ potted plants were grown without giving a top dressing in Kyushu Okinawa Agricultural Research Center, Chikugo, Japan, according to the method of Wada et al (2011). At flowering, the potted plants grown in field were transferred to the walk-in environmentally-controlled growth chamber (26/22°C, 70/80% relative humidity, and 750 μmol photons m −2 s −1 photosynthetically active radiation [PAR]) set at the plant canopy using light emitting plasma (LEP) lamps (STA 41-02, Stray Light Optical Technologies, Inc., IN, the US) with a photoperiod of 13 h day/11 h night.…”

Countermeasures for heat damage in rice grain quality under climate change

“…It has been shown that the inner endosperm cells, where a high frequency of chalky ring was observed, maintained endosperm cell turgor by osmotic adjustment under shortterm dry wind conditions prior to the chalky formation, which sustains the kernel development (Wada et al, 2011). And, a temporal reduction in starch biosynthesis with no starch degradation also occurred at osmotic adjustment during short-term dry wind conditions (Wada et al, 2014).…”

“…Also, it has been widely recognized that foehn (dry high-speed wind) causes an excessive cuticular transpiration from the panicle that subjects the plants to the short-term shoot water deficit, resulting in spikelet sterility (Ishihara et al, 1990;Muramatsu, 1982;O'Toole et al, 1984). Aside from the spikelet sterility at flowering, dry wind occurred during the ripening substantially increases ring-shaped chalky kernels, called milky-white rice, and contrastingly lowers perfect rice (Ishihara et al, 2005;Wada et al, 2011). It is also known that rice plants during the middle ripening stage are particularly vulnerable to wind-induced water deficit, compared with other ripening stages (Oya & Yoshida, 2008).…”

“…recently, the direct turgor measurements using a cell pressure probe have further extended the understanding of dry wind-induced chalky ring formation at moderately low water potential (Wada et al, 2011(Wada et al, , 2014. It has been shown that the inner endosperm cells, where a high frequency of chalky ring was observed, maintained endosperm cell turgor by osmotic adjustment under shortterm dry wind conditions prior to the chalky formation, which sustains the kernel development (Wada et al, 2011).…”