Diurnal Changes in Maize Leaf Photosynthesis

Abstract

Maize (Zea mays L. cv. Pioneer 3184) leaf elongation rate was measured diurnally and was related to diurnal changes in the activities of sucrose metabolizing enzymes and carbohydrate content in the elonpting portion of the leaf. The rate of leaf elongation was greatest at midday (1300 hours) and was coincident with the maximum assimilate export rte from the distal portion of the leaf. Leaf elongation during the light period accounted for 70% of the total observed increase in leaf length per 24 hour period. Pronounced diurnal fluctuations were observed in the activities of acid and neutral invertase and sucrose phosphate synthase. Maximum activities of sucrose phosphate synthase and acid invertase were observed at 0900 hours, after which activity declined rapidly. The activity of sucrose phosphate synthase was substantially lower than that observed in maize leaf source tissue. Neutral invertase activity was greatest at midday (1200 hours) and was correlated positively with diurnal changes in leaf elongation rate. There was no significant change in the activity of sucrose synthase over the light/dark cycle. Sucrose accumulation rate increased during a period when leaf elongation rate was maximal and beginning to decline. Maximum sucrose concentration was observed at 1500 hours, when the activities of sucrose metabolizing enzymes were low. At no time was there a significant accumulation of hexose sugars. The rate of starch accumulation increased after the maximum sucrose concentration was observed, continuing until the end of the light period. There was no delay in the onset of starch mobilization at the beginning of the dark period, and essentially all of the starch was depleted by the end of the night. Mobilization of starch in the elongating tissue at night could account for a significant proportion of the calculated increase in the tissue dry weight due to growth. Collectively, the results suggested that leaf growth may be controlled by the activities of certain sucrose metabolizing enzymes and may be coordinated with assimilate export from the distal, source portion of the leaf. Results are discussed with reference to diurnal photoassimilation and export in the distal, source portion of the leaf.Regulation of leaf growth and development is a critical factor in crop productivitiy because these processes ultimately determine the total photosynthetic area available for light interception and carbon assimilation. The growth and development of maize leaves occurs in a manner unique to monocots; leaf growth

Annual metabolic carbon balance of the seagrass Posidonia oceanica: the importance of carbohydrate reserves

“…solar cycle). This is in contrast with some findings in terrestrial plants, especially crop plants, which clearly show daily fluctuations (Rufty et al 1983, Sicher 1984, Kalt-Torres & Huber 1987. The absence of nighttime sucrose depletion in leaves of other seagrass species (Zostera marina; Zimmerman et al 1995) suggests that seagrasses probably have a pool of carbohydrates high enough to buffer the daily fluctuations in light availability without great changes, since most of the variability in carbohydrate content is reflected at a seasonal scale.…”

Gene Expression of Enzymes for Starch and Sucrose Metabolism and Transport in Leaf Sheaths of Rice (Oryza sativaL.) during the Heading Period in Relation to the Sink to Source Transition

“…As described above, an important difference between these two leaf sheaths is that the flag leaf sheath was elongating until about a week before heading but the second leaf sheath was not. In young maize leaves SuSy activity was highest in the elongation zone (Kalt-Torres and Huber 1987). High SuSy mRNA level in the flag leaf sheath, concomitant with its elongation, therefore suggests that imported sucrose is utilized for the sheath's own growth.…”

Phosphorylation of Serine-15 of Maize Leaf Sucrose Synthase (Occurrence in Vivo and Possible Regulatory Significance)

“…Mature maize leaves contain a low activity of SuSy (Kalt-Torres and Huber, 1987;Nguyen-Quoc et al, 1990), which is probably confined to the vascular tissues (Geigenberger et al, 1993;Nolte and Koch, 1993). The SuSy in source leaves was also 32 P-labeled (data not shown).…”