Effects of High Temperature and Water Deficit on Photosystem II in Hordeum vulgare Leaves of Various Ages

Structural and functional characteristics of photosystem II (PSII) were examined in leaves of 4-, 7-, and 11-day-old barley seedlings exposed to high temperature (40°C, 3 h) and water deficit (replacement of nutrient medium with 3% PEG 6000 solution, 45 h). In young seedlings, the effective quantum yield of PSII photochemical reactions decreased upon heat treatment but did not change after dehydration. Both stressful factors diminished the Q _B-reducing capacity of PSII in 4- and 7-day-old plants. This was caused by the increase in the reduction level of plastoquinone and by the impairment of the Q _B-binding site of the D1 protein. The increase in the content of plastoquinol after the heat shock was due to the impaired oxidizing capacity of cytochrome f (Cyt f). The dehydration did not alter the content of functionally active Cyt f but elevated the microviscosity of the lipid bilayer in thylakoid membranes, which presumably impeded the lateral diffusion of plastoquinones and reduced their reoxidation rate. The heating and dehydration of old leaves reduced the amount of -type PSII reaction centers, thereby inhibiting the linear electron transport. It is concluded that PSII responses to heat treatment and water deficit are subject to variations depending on leaf age. Measurements of the redox potentials for plastoquinones, Cyt f, and cytochrome b ₅₅₉ upon senescence, hyperthermia, and water deficit allowed us to propose that heat and water stresses activate cyclic electron transport around PSII.     

Organisation of Photosynthetic Apparatus of Triticale in Relation to Productivity

Chlorophyll (Chl) content, photochemical activity of chloroplasts as well as photosynthetic and crop productivity were studied in different winter hexaploid Triticale (xTriticosecale Witt.) lines and their F₁ hybrids. Heterosis enhanced Chl content, photosynthetic potential, photosynthetic productivity, and grain yield only in several F₁ hybrids of Triticale. Indication in some genotypes of close correlations among morphological structure, Chl content, photochemical activity of chloroplasts, photosynthetic potential, and plant productivity may be used in breeding practice of Triticale. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Pool of Chlorophyllous Pigments in Barley Seedlings of Different Ages under Heat Shock and Water Deficit

The effects of a high temperature (3 h, 40°C) and water deficit (45 h on 3% PEG 6000) on the pool of chlorophyllous pigments in the leaves of 4-, 7-, and 11-day-old barley (Hordeum vulgare L.) seedlings were studied. Heating resulted in a decrease in the total content of chlorophylls (Chl) (a + b) in 4-day-old plants but not in the older leaves. Water deficit induced an increase in the pigment content in young seedlings but reduced it in the leaves of 11-day-old plants. In young seedlings, hyperthermia and dehydration affected similarly Chl (a + b) degradation, leading to a marked inhibition of the chlorophyllase (Chlase) activity hydrolyzing Chl to chlorophyllides and phytol. In old leaves, an activation of this enzyme was observed. The stress factors under study affected different stages of pigment biosynthesis. High temperature inhibited the activity of dark and light stages of Chl(a + b) biosynthesis. Dehydration did not change markedly the resynthesis of protochlorophyllide, while the enzymes of the light stage of Chl biosynthesis were activated in young but inhibited in old barley leaves. The results thus obtained allowed us to conclude that heat treatment and dehydration specifically affected the Chl biosynthesis. At the same time, the Chlase response was nonspecific.     

Biogenesis of photosynthetic apparatus under the inhibition of energy processes in de-etiolated seedlings of barley (Hordeum vulgare L.)

Transformation of protochlorophyllide forms in etiolated barley seedlings and biogenesis of photosynthetic apparatus in greening leaves of 7-day-old etiolated barley seedlings (Hordeum vulgare L.) were studied under the inhibition of energy processes during illumination. Repression of electron transport between photosystem 2 and 1 (PS2 and PS1, respectively) with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) inhibited the photochemical activity of PS2 but did not affect chlorophyll biosynthesis and ATP content in leaves compared to the control. Inhibition of mitochondrial electron transport with sodium azide increased relative content of nonphotoactive protochlorophyllide in etiolated leaves, decreased the content of ATP, chlorophylls, and carotenoids and completely suppressed the functional activity of PS 2. The inhibitor of glycolysis sodium fluoride affected all the parameters even more strongly. We observed synchronism in the accumulation of chlorophylls and carotenoids during greening for all inhibitor variants other than fluoride (correlation coefficient, r, equal to 0.98, 0.97, 0.97, and 0.47 with the significance level of 0.01; 0.015; 0.015, and 0.27 for control, diuron, azide, and sodium fluoride, respectively). The change in chlorophyll content under the influence of inhibitors positively correlated with the amount of ATP in the leaf tissue (for 24 h greening, r = 0.97 with significance level of 0.015). We suggest that sources of ATP involved in the synthesis of chlorophyll during greening of etiolated barley seedlings are mostly of non-plastid origin.     

Specifity of Genetic Determination of Content of Photosynthetic Pigments in Triticale

Lines of winter hexaploid Triticale and their F₁ and F₂ hybrids differing in morphological structure, pigment contents, photosynthetic productivity, and grain crops were studied. F₁ hybrids received by crossing of Triticale lines contrasting in pigment contents showed in some cases a heterosis effect for chlorophyll (Chl) content per unit leaf area. Variation analysis demonstrated a polygenic control of Triticale pigment contents, and different rate of increase in F₂ generation. We found maternal type of heritability of Chl b content and Chl content in light-harvesting complex of photosystem 2.     

Tissue-Specific Features of Pigment Biogenesis in Coleoptiles of Greening Etiolated Seedlings of Cereals

Biogenesis of the pigment apparatus was studied in coleoptiles of postetiolated barley seedlings (Hordeum vulgare L.) and triticale (Triticale), differing in chlorophyll content, during growing in a “ light-darkness” regime with a 16-h photoperiod. Photoactive protochlorophyllide with a fluorescence maximum at 655 nm (Pchlide655), which accumulates in coleoptiles of etiolated seedlings, was converted in the light into a chlorophyll pigment with a fluorescence maximum at 690 nm (excitation at 440 nm, temperature ?196°C). The spectral transition 690 nm → 675 nm forms was completed in darkness for 15 min illumination. There was almost no resynthesis of new portions of Pchlide655 in coleoptiles under darkness conditions, even after a 5–6-h darkness period after brief illumination of seedlings with flashes of white light. Chlorophyllide (Chlide) formed from Pchlide655 was not esterified and was destroyed both in the light (4 h, 1.0–1.5 klx) and darkness. In coleoptiles of greening etiolated seedlings, chlorophyll formation started only by 24 h of illumination. The instability of the chlorophyll pigment formed after etiolation indicates that plastids of coleoptiles do not contain the system of chlorophyll biosynthesis centers typical of leaves, which are bound to membranes and protect pigment from destruction.     

Effect of kinetin on the state of the protochlorophyll pigment in the inner membrane system of etioplasts

Effect of kinetin on the state of etioplast inner membrane system in etiolated barley (Hordeum vulgare L.) seedlings was studied by quantifying changes in the ratio of fluorescence intensity of the long-wave form of protochlorophyllide (Pchlde) to that of its short-wave form (Pchlde657 and Pchlde633, respectively) in the leaf low-temperature spectra. Application of kinetin (20 μg/ml, sprinkling) resulted in a decrease of the Pchlde657/Pchlde633 ratio, and the heat shock (3 h at 40°C) strengthened this effect of kinetin. The change in the Pchlde657/Pchlde633 ratio induced by kinetin did not depend on the seedling age within the range of 5–7 days. Possible mechanisms of the kinetin effect on the etioplast membrane systems are discussed.     

Changes in the photosynthetic apparatus during fusarium wilt of tomato

Development of fusarium wilt was studied in 4-to 6-month-old tomato plants (Lycopersicon esculentum L., cv. Kunera). It was shown that the development of this disease could follow two patterns. When the wilt developed slowly (type I disease), the mycelium of Fusarium oxysporum fungus partly blocked the xylem and grew extensively within parenchyma. When the wilt developed fast (type II syndrome), the occlusion of both xylem and phloem was observed; the xylem sap circulation was suppressed and, consequently, tomato plant tissues were dehydrated. The development of type I and type II diseases led to suppression of photosynthetic activity in plants. In the case of slow wilt (type I), both light and dark stages of photosynthesis were damaged. This was evident from the decrease in the effectiveness of light harvesting and charge separations in the reaction centers of photosystem II (PSII), suppression of electron transport at the acceptor side of PSII, and the decrease in activity of Rubisco. In the case of fast wilt (type II), the Rubisco activity did not change, and photochemical activity of chloroplasts was suppressed to a smaller degree than during type I fusarium wilt. The decrease in the rate of linear electron transport in tomato leaves was mostly due to inhibition of electron flow at the acceptor side of PSII. The data obtained suggest that photosynthetic activity in tomato plants is suppressed by different mechanisms depending on the developmental pattern of fusarium wilt.     

Relations between Photosynthetic Pigment Accumulation and Microsporogenesis in Secale, Triticale, and Secalotriticum

The accumulation of photosynthetic pigments in underflag and flag leaves as well as the process of microsporogenesis in lines of tetraploid Secale, hexaploid Triticale, and hexaploid Secalotriticum were studied. Significant positive correlations were found between the amounts of chlorophyll a (Chl a), carotenoids (Car), Chl a/b ratio, and the normal proceeding of meiosis. High probability of paternal type of inheritance of specifities of meiosis of pollen mother cells and variation in photosynthetic pigments during plant transition from the stalk-shooting to heading stage were demonstrated.     

Degradation of Chlorophyll in the Leaves of Reed Fescue (Festuca arundinacea) under the Action of Volatile Organic Compounds and Benzo(a)pyrene

Biology Bulletin - The pathways of chlorophyll a and b degradation were studied in the leaves of reed fescue (Festuca arundinacea) under the action of volatile organic compounds (pentane, hexane,...