Analysis of fluorescence transients of DCMU-treated leaves of Triticum species to provide estimates of the densities of photosystem II reaction centres

Abstract

The fluorescence of the chlorophyll associated with photosystem II was studied in seedling and flag leaves of Triticum species. Seedling leaves of the diploid species T. urartu had higher values of t (the normalised area over the fluorescence induction curve of DCMU treated leaves) than those of the other species studied which included hexaploid T. aestivum. However this difference was not evident when leaves were grown in a low light intensity (40 µmol quanta of photosynthetically active radiation m(-2) s(-1)). The smaller total number of chlorophyll molecules per photosystem II reaction centre (chl/RCII) in T. urartu (177) as compared with the other species (mean 234) was deduced from the observed differences in t. As a consequence of its lower chl/RCII, despite slightly lower chlorophyll content (mg m(-2)), T. urartu had a greater density of reaction centres than the other species (2880 cf 2230 nmol m(-2) of leaf). Consistent with the lower chl/RCII of T. urartu, it had a higher chlorophyll a/b ratio than the other genotypes. Seedling leaves of T. urartu had higher light saturated rates of photosynthesis than those of the other species, when grown at high light, a difference associated with reaction centre density.In flag leaves, when the complications due to variable development and senescence patterns were eliminated, t of the diploid species including T. urartu was lower than that of T. aestivum. The lower apparent chl/RCII of T. urartu arose partly because the molar extinction coefficient of the chlorophyll in the leaves of T. urartu was greater than in T. aestivum. However, the density of PS II reaction centres was slightly lower for the diploid species studied because their chlorophyll contents were lower than the hexaploids.The validity of the method for estimating chl/RCII from fluorescence transients is discussed. The possibility is considered that the difference in apparent chl/RCII of flag and seedling leaves of R. urartu as compared to the other five genotypes is a consequence of its different adaptive response to the spectral quality of the light.

Estimation of the light distribution between photosystems I and II in intact wheat leaves by fluorescence and photoacoustic measurements

“…The results presented here show that under the conditions used for the fluorescence induction method for measuring PSII unit size the two photosystems are very nearly at balance and therefore the previous use of the factor /3 = 0.5 was close to the true value [19,21,23]. This result is also in accord with the measurement of /3 in isolated chloroplasts of various species, using a completely different procedure [22].…”

“…We were concerned with the possibility that the results of our measurements, while applicalbe to the steady-state situation, involving some adaptation to the prevailing light conditions, may not be correct for darkadapted leaves. Dark-adapted leaves are used for fluorescence induction experiments to determine the unit size of photosystem II [19,23]. Thus, a rapid photoacoustic measurement of a previously dark adapted leaf was attempted, as described below.…”

Variation in thylakoid proteins and photosynthesis in Syrian landraces of barley

“…Morgan & Austin (1986) showed that there were differences in chlorophyll a:b ratio and in the estimated numbers of CCII complexes per unit area of leaf between seedling and flag leaves of wheat grown under con- trolled environment and field conditions respectively . In diploid wheat species, as compared to hexaploid wheat, high chlorophyll a : b ratio is associated with a smaller ratio of antenna chlorophyll (LHCP) to that in the core complex of photosystem II (CCII) and also with a higher capacity for photosynthetic electron transport (Austin et al ., 1988 ;Watanabe et al ., 1992) .…”

“…Some plants adapt to variation in the environment and modify their chlorophyll proteins to capture light energy in a more efficient way in order to prevent excess solar radiation which, particularly during drought and heat stress, can cause photoinhibition (Lichtenthaler et al ., 1982a(Lichtenthaler et al ., , 1982b . Morgan & Austin (1986) have shown that, in wheat, high rates of light-saturated photosynthesis are associated with the density of photosystem II reaction centres on the thylakoid membranes. This character is associated with low chlorophyll content, high chlorophyll a : b ratio and high rates of electron transport through PSII (Austin et al ., 1987) .…”

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

“…Fluorescence collected by an optical fiber was measured at wavelength above 700 nm. The yield of fluorescence is related to the density of intact photosystem II reaction centers [14].…”