Assimilate Partitioning Within Floret Components of Contrasting Rice Spikelets Producing Qualitatively Different Types of Grains

Abstract

Grain quality, soluble and insoluble carbohydrate contents, and activities of two key enzymes (sucrose synthase and invertase) involved in starch synthesis in the endosperm were measured in the components of the fertile florets of spikelets located at the tip of the uppermost primary branch (top spikelet), and the penultimate position of the lowermost primary branch (basal spikelet) of rice panicles during the period begining some days before anthesis to maturity. The basal spikelet, which reached anthesis a week after the top spikelet, produced a partially filled poor quality grain in contrast to the good quality high density grain produced by the latter. Sucrose was the major translocatable sugar in the organs of the fertile florets of both top and basal spikelets, and poor grain filling of the latter was not caused by deficiency of this material due to any resistance in supply in the external protective organs. The activities of the sucrose synthase and invertase were higher and lower respectively, in the endosperm cells of the top spikelet compared with the basal spikelet. We conclude that poor synthesis of the starch leading to partial grain filling in the basal spikelet is due to a lower activity of sucrose synthase.

High ethylene production slackens seed filling in compact panicled rice cultivar

“…1). Similar difference between dry matters partitioning of contrasting spikelets of rice panicle was reported earlier (Patel and Mohapatra 1996;Kato and Takeda 1993). Therefore, advantage accrued to the panicle of OR-1920-7 on account of larger grain number or sink size is marginalized because of the loss of individual grain weight and quality.…”

“…4), the correlations between the chemical and rates of cell division and grain growth were stronger (Table 3). We reported previously that inferior basal spikelets of rice panicle produce more ethylene compared to the dominant apical spikelets and rates of cell division and dry matter accumulation as well as the activities of enzymes for starch synthesis was slower in the former than in the latter (Patel and Mohapatra 1996;Naik and Mohapatra 2000;Mohapatra et al 2009). In the present work, it was evident that high ethylene production owing to spatial disadvantage or genetic difference restricts assimilate partitioning for the spikelets (Fig.…”

“…In contrast, spikelet development on the lower branches is impacted considerably during the early part of post anthesis period (Ishimaru et al 2003) resulting in the formation of partially filled poor quality grains (Mohapatra et al 1993). The early loss of efficiency of the basal grains to use assimilates is linked to weaker activities of the enzymes related to starch synthesis (Nakamura and Yuki 1992;Kato 1995;Patel and Mohapatra 1996;Smidansky et al 2003). Ethylene production in the flowering organs significantly affects the activities of the enzymes Mohapatra et al 2009).…”

Apoplasmic assimilates and grain growth of contrasting rice cultivars differing in grain dry mass and size

“…The developing endosperm remains confined within the embryonic space (apoplasmic space; Oparka and Gates 1981a, b;Thorne 1985;Weber et al 2005) and does not have any alternate source of supply for assimilates. Endosperm cell number increases rapidly during this period and positional disadvantage on panicle axis restricting cell multiplication limits seed filling and weight in an inferior caryopsis (Patel and Mohapatra 1996). The low sink efficiency of such caryopses might have resulted in accumulation of the unused assimilates in the pericarp and endosperm (Fig.…”

Leaf gas exchange and yield of three upland rice cultivars

“…In rice, the grain size is determined by the hull space, which is a stable varietal character (Matsushima, 1970;Peng et al, 2000;Santos et al, 2006), and grain filling is generally sink-limited (Mohapatra et al, 2004;Patel & Mohapatra, 1996), indicating that the sink size and the sink strength are more important than A. Our results indicate that in 'Primavera', matter accumulation in the grain seems to be dependent on post-flowering photosynthesis, as A was constant between 74 (FL) and 89 DAE (MA) (Figure 2a), when medium temperatures were as close as to 25 °C (Figure 5a).…”