Functional and molecular changes in the photosynthetic apparatus during senescence of flag leaves from field‐grown barley plants

Abstract

Changes in the function and composition of the photosynthetic apparatus were analysed during maturation and senescence of barley (Hordeum vulgare L.) flag leaves under field conditions. At about 8 d post‐antbesis. photo‐synthetic capacity, measured as oxygen evolution under light‐saturating conditions, and the D1 protein level started to decrease. At about 14 d post‐anthesis, the pigment content, photosystem II efficiency (Fv/Fm) and levels of cytochrome f and the large subunit of ribulose‐1,5‐bis‐phosphate carboxylase started to decline. The levels of cytochrome b559 and the small subunit of ribulose‐1,5‐bis‐phosphate carboxylase decreased later, at about 22 d post‐anthesis. High levels of the light‐harvesting complex of pliotosyslem II were still detectable at an even later stage of senescence, at 26 d post‐anthesis. There were also differences in the kinetics of the declines in the levels of transcripts coding for components of the photosynthetic apparatus. rbcS mKNA abundance had already decreased when flag leaves reached their final lengths, at about 4 d post‐unthesis, whereas levels of psbA and petC transcripts did not decrease until 16 d post‐anthesis. In contrast, a senescence‐related transcript, pHvS40 (Becker & Apel 1993), accumulated in the flag leaves 14 d post‐anthesis. Several senescence‐related processes which differ in their kinetics are described. The interrelationships among these processes and their regulation are discussed.

Different effects of dark treatment on pigment composition and photosystem I and II activities in intact cotyledons and primary leaves of Cucurbita pepo (zucchini)

“…The latter is due to an enhanced stability of the light-harvesting complexes containing Chl b in comparison to the reaction center complexes including exclusively Chl a (Humbeck et al 1996;Miersch et al 2000). In agreement with the above results, we showed a stronger decrease in Chl a content as compared to Chl b in both cotyledons and primary leaves during natural senescence, thus leading to a reduction in the Chl a/b ratio (Table 1).…”

“…2a) which could be accounted for by the drastic decline in pigment content. A similar result was observed previously in senescing barley leaves where the F V /F M ratio decreased only at a later point of time (Humbeck et al 1996;Miersch et al 2000).…”

A Comparison of Regression Techniques for Estimation of Above-Ground Winter Wheat Biomass Using Near-Surface Spectroscopy

“…The correlation between AGB and red-and near-infrared-band VIs is low in this study (Table 4). This may be because, during the reproductive stage, photosynthesis and the near-infrared reflectance [84] both clearly decrease (Figure 2), reducing the correlation between AGB and the red-and near-infrared-based VIs. This result is consistent with the results of a previous study [17].…”

Physiological, anatomical and biomass partitioning responses to ozone in the Mediterranean endemic plant Lamottea dianae

“…The observed physiological responses are very similar to those taking place during senescence. A decline in the stromatic protein Rubisco is considered a key senescence event leading to reduced photosynthetic activity (Crafts-Brandner et al, 1990), while degradation of thylakoid proteins and important effects in the light harvesting system such as a decline in F v :F m are usually delayed to later senescence phases (Humbeck et al, 1996). In fumigated leaves of the present experiment, there was a tendency to reduce the light energy used in photochemistry (indicated by a significant decrease in F PSII and a reduction in qP) at the expense of heat dissipation (NPQ increases).…”