Physiological characteristics of a functional stay-green rice “SNU-SG1” during grain-filling period

Abstract

Functional stay-green has been regarded as a promising characteristic to be introduced for improving rice yield potential. A functional stay-green rice "SNU-SG1" that was identified from japonica rice collections was compared with two regular high-yielding rice cultivars (HYVs) for the temporal change of leaf chlorophyll, soluble protein, and root activity, and nitrogen accumulation and remobilization during the grain-filling period. SNU-SG1 had slower decreasing rate and maintained higher concentration of chlorophyll and soluble protein in upper four leaves during the grain-filling period than HYVs "Suweon490" and "Andabyeo", revealing a typical stay-green characteristic. Even though SNU-SG1 remobilized almost the same proportion of N accumulated before heading as HYVs to grain, it maintained much higher leaf N concentration due to the significantly higher N accumulation that is ascribable to the higher root activity sustenance during grain-filling period. The functional stay-green trait of SNU-SG1 seems to stem not only from the genetic control preventing chlorophyll degradation but also from the higher capacity to absorb N from soil due to the sustained strong root activity during grain-filling period. SNU-SG1 exhibited higher crop growth rate during late grain-filling period than HYVs, resulting in higher grain-filling percentage and non-structural carbohydrate re-accumulation in the stem at the final stage of grain filling. It is concluded that SNU-SG1 has a promising trait "functional stay-green" contributable to rice yield potential improvement through the improved grain filling.The functional stay-green trait during grain filling that results from a delay in the onset of leaf senescence or a slower decrease of chlorophyll content and photosynthetic activity (Thomas and Howarth 2000) will probably extend the assimilatory capacity of the canopy and might contribute to higher grain yields (Gwathmey et al. 1992). Spano et al. (2003) reported that functional stay-green mutants of durum wheat maintained longer photosynthetic activity, had higher seed weights, and yielded more grain than the parental genotype. Luo (2006) also reported a new stay-green wheat cultivar "CN17" with delayed leaf senescence maintained longer and higher photosynthetic competence compared with the control cultivar and this aspect was correlated with the difference in chloroplast development.Grain filling and leaf assimilation sustenance are usually conflicting processes in monocarpic cereal crops as the amount of N absorbed during grain filling is much smaller than the amount of N accumulated in mature grains. Thus, a large part of grain N is remobilized from vegetative organs especially from leaf blades to the developing grain (Mae 1997), causing leaf senescence and decrease of photosynthesis after flowering. As plant leaves, particularly chloroplasts, are sites of protein accumulation, mobilization of chloroplast protein is a central metabolic activity in leaf senescence and most of the mobilizable protein in a leaf is soluble protein...

Improving yield potential of tropical rice: Achieved levels and perspectives through improved ideotypes

“…The environment effects, in turn, were partly related to variation in terminal senescence. Consequently, considerable scope may exist in improving rice RUE, and thus increasing biomass, both in terms of a genotypic trait (Reynolds et al, 2000) and as a result of delayed terminal senescence, which in turn is controlled both genetically (Thomas and Howarth, 2000;Fu et al, 2009) and by the environment (our results; Gregersen et al, 2013).…”

“…Functional stay-green has been suggested as a possible solution to these constraints (Thomas and Howarth, 2000;Fu et al, 2009). Our simulations suggest that full stay-green (maintenance of the maximal LAI until maturity), although increasing YP theoretically, would require unreasonably high amounts of N uptake and involve very high R m .…”

“…But a partial stay-green scenario (Senescence 2 scenario), with leaf canopy tops unaffected by terminal senescence, would increase potential biomass production nearly equally and require less N uptake. Fu et al (2009) compared a stay-green type japonica line (SNU-SG1) with terminally senescing HYVs and found that they did not differ in the fraction of shoot N relocated to the panicle, about 50-60%. Norman et al (1992) reported an N harvest index of about two-thirds.…”

“…Consequently, crop growth rates (CGR) tend to be low during grain filling and even negative towards maturity (Schnier et al, 1990a;Dingkuhn et al, 1990). This phenomenon has several causes: (1) the increasing burden of maintenance respiration (R m ) which depends on biomass and particularly, its N content (Penning de Vries et al, 1989); (2) terminal leaf senescence which reduces photosynthesis but is necessary to provide the panicle with the mobilized N to produce grain (Sinclair and Sheehy, 1999); and (3) the apparent inability of the crop to achieve substantial post-floral N uptake (Schnier et al, 1990a,b;Fu et al, 2009), or alternatively to store significant N reserves in organs other than leaves. Consequently, even additional N application late in the season does little to mitigate leaf area loss and sustain high canopy photosynthetic rates during grain filling (Dingkuhn et al, 1992a).…”

Natural leaf senescence: probed by chlorophyll fluorescence, CO2 photosynthetic rate and antioxidant enzyme activities during grain filling in different rice cultivars

“…Due to the few number of sufficient spikelet's even the stay green cultivars failed to produce sufficient filled-grain. Instead the newly synthesized carbohydrate started to move to the stem and deposited there (Peng et al 2005;Fu et al 2009). The probability to improve rice yield was more with the cultivars that possessed sufficient numbers of spikelets and maintained greater chloroplast structural and functional ability during grain filling stage.…”