Effects of periodic fluctuations of photon flux density on anatomical and photosynthetic characteristics of soybean leaves

Abstract

The development of soybean leaves grown at fluctuating photon flux density between 100 and 1500μM m(-2)s(-1) with a period of 160 sec were compared to leaves developed under continuous light with the same mean photon flux density. Number of epidermal cells and stomata, leaf area and specific leaf weight were not affected by the periodic fluctuation of photon flux density. Chloroplastic pigment concentration and chlorophyll fluorescence reveal some photoinhibitory effects of the high photon flux density phase. Stomatal and internal CO2 conductance and the quantum yield were not affected by the light regime. In contrast ribulose 1.5 bisphosphate carboxylase/oxygenase activity before in vitro activation by CO2 and Mg(++) was stimulated by the periodic illumination whereas the total amount of the enzyme and the internal leaf CO2 conductance remained steady. In conclusion, there was no major difference between leaves of plant grown either under a steady or under a periodic fluctuation of the photon flux density except some photoinhibitory symptoms under fluctuating illumination, and a higher in vivo level of activation of the Rubisco.

Photosynthetic Induction State of Leaves in a Soybean Canopy in Relation to Light Regulation of Ribulose-1-5-Bisphosphate Carboxylase and Stomatal Conductance

“…Photosynthetic acclimation in response to the gradient in PFD within the canopy as well as age-dependent changes, results in differences in photosynthetic capacity, specific leaf weight, and rubisco content in leaves at the top as compared to leaves within a canopy (8). The decreasing photosynthetic capacity, rubisco content, and changes in Chl to rubisco ratios with depth in the canopy are similar to results obtained when soybeans were grown at different photon flux densities (6,22,25). This sun-shade differentiation limits the capacity of lower leaves to utilize high PFD.…”

“…Under steady-state conditions, initial rubisco activities and photosynthetic rate usually exhibit similar light-dependent responses in soybean (22,25). However, initial rubisco activities in soybean leaves were maintained at higher values in a fluctuating than in a constant light regime where both had the same average PFD (6). This result can be explained by the faster increase than decrease in initial rubisco activities following increases and decreases in PFD, respectively (13,23).…”

Influence of photon flux density and fluctuation on the nitrogen fixing Glycine max (L Merr)-Bradyrhizobium japonicum symbiosis in a controlled environment

“…This phenomenon may be specific to soybean since it was not detected on peas transferred from 0.50 to 0.80 mmol photons m -2 ·s -1 (Sheikholeslam et al, 1980) or french beans transferred from 0.04 to 0.11 mmol photons m -2 ·s -1 (Antoniw and Sprent, 1978). Its mechanism is not known; it differs with the early limitation of young plant nodulation by excess light (Fred et al, 1938;Orcutt and Fred, 1935) which has recently been attributed to N limitation of legumes depending exclusively on N 2 fixation (Williams and Phillips, 1980 (Gaudillère et al, 1987).…”

Controlled periodic illumination in semiconductor photocatalysis

“…Its investigation in the field of photosynthesis research which is characterised by photon saturation during TON precedes photocatalysis and is also concerned with enhancement of efficiency. Earlier results in this area of research indicate an improved quantum yield under CPI [41] however, there are reports of equivalent yields under continuous and periodic illumination from other studies [42,43].…”