Changes in photosynthetic apparatus during dark incubation of detached leaves from control and ultraviolet-B treatedVigna seedlings

Abstract Background and Aims Ultraviolet-B radiation (UV-B) radiation damages the DNA, cells and photosynthetic apparatus of plants. Plants commonly prevent this damage by synthetizing UV-B-protective compounds. Recent laboratory experiments in Arabidopsis and cucumber have indicated that plants can also respond to UV-B stress with endopolyploidy. Here we test the generality of this response in natural plant populations, considering their monocentric or holocentric chromosomal structure. Methods We measured the endopolyploidy index (flow cytometry) and the concentration of UV-B-protective compounds in leaves of 12 herbaceous species (1007 individuals) from forest interiors and neighbouring clearings where they were exposed to increased UV-B radiation (103 forest + clearing populations). We then analysed the data using phylogenetic mixed models. Key Results The concentration of UV-B protectives increased with UV-B doses estimated from hemispheric photographs of the sky above sample collection sites, but the increase was more rapid in species with monocentric chromosomes. Endopolyploidy index increased with UV-B doses and with concentrations of UV-B-absorbing compounds only in species with monocentric chromosomes, while holocentric species responded negligibly. Conclusions Endopolyploidy seems to be a common response to increased UV-B in monocentric plants. Low sensitivity to UV-B in holocentric species might relate to their success in high-UV-stressed habitats and corroborates the hypothesized role of holocentric chromosomes in plant terrestrialization.

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Responses of Rice and Pea Plants to Hardening With Low Doses of Ultraviolet-B Radiation

Functional Plant Biology ◽

10.1071/pp9940563 ◽

1994 ◽

Vol 21 (5) ◽

pp. 563 ◽

Cited By ~ 13

Author(s):

J He ◽

LK Huang ◽

WS Chow ◽

MI Whitecross ◽

JM Anderson

Keyword(s):

Oryza Sativa L ◽

Photosynthetic Apparatus ◽

Ultraviolet B ◽

Water Soluble ◽

Rice Cultivars ◽

Unit Leaf ◽

Hardening Treatment ◽

Uv Absorbing Compounds ◽

Soluble Enzymes ◽

Photosynthetic Properties

Responses of two rice cultivars (Oryza sativa L. cw. Er Bai Ai and Lemont) and a pea plant (Pisum sativum L. cv. Greenfeast) to low daily doses of ultraviolet-B (UV-B) radiation were measured to explore mechanisms underlying UV-B tolerance. On hardening of rice plants, cv. Er Bai Ai produced more UV-absorbing compounds than cv. Lemont; however, cv. Lemont produced more water-soluble proteins, which may be related to its greater UV-B tolerance. These responses occurred without apparent deleterious effects on the photosynthetic properties of rice leaves. In contrast, the same hardening doses caused damage to pea plants, as indicated by decreases in photosynthetic quantum yield, maximum photosynthetic capacity and chlorophyll content per unit leaf area, as well as water-soluble and total protein contents. The acquired tolerance of the two rice cultivars to a subsequent high UV-B dose increased with the duration of the hardening treatment. In contrast, the 'hardening' treatment exacerbated the damage to the photosynthetic apparatus of pea plants subsequently exposed to a high UV-B dose. It appears that for defence against UV-B radiation, cv. Er Bai Ai relies more upon the synthesis of UV-absorbing compounds, while cv. Lemont depends more upon the synthesis of protective, water-soluble enzymes; however, neither strategy seems to operate effectively in pea plants.

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Recovery of the photosynthetic apparatus from photoinhibition during dark incubation of the green alga Dunaliella salina

Functional Plant Biology ◽

10.1071/pp99004 ◽

1999 ◽

Vol 26 (7) ◽

pp. 679 ◽

Cited By ~ 5

Author(s):

Jürgen E. W. Polle ◽

Anastasios Melis

Keyword(s):

Reaction Center ◽

Dunaliella Salina ◽

De Novo ◽

Light Harvesting ◽

Photosynthetic Apparatus ◽

D1 Protein ◽

Dark Incubation ◽

Chl A ◽

Lag Period ◽

Stressed Cells

The light-independent recovery of the photosynthetic apparatus from photoinhibition was monitored upon a transition of irradiance-stressed Dunaliella salina Teod. to darkness. Upon dark incubation, the chlorophyll (Chl) a /Chl b ratio of the cells decreased promptly with a half-time of 2.5 h from about 12:1 to about 5:1. In contrast, dark incubation of control cells resulted in only a negligible change of the Chl a /Chl b ratio. During dark incubation of irradiance-stressed cells, the level of the Chl a and b light-harvesting proteins of photosystem II (PSII) increased, a change accompanied by alterations in the composition of these light-harvesting proteins. The amount of photodamaged PSII, measured from the relative amount of a 160 kDa protein complex which contains the photodamaged D1 reaction center protein, decreased during dark incubation after an initial lag period. Concomitantly, the amount of functional PSII, measured from the 32 kDa form of D1, increased slightly in the dark. The results show that, in the dark, photodamaged D1 is slowly removed upon degradation from the thylakoid membrane and replaced by a de novo synthesized D1 protein. The amount of reaction center proteins and number of photochemically active PSI centers increased in the dark. These results suggest that thylakoid membranes of irradiance-stressed D. salina exist in a state of dynamic flux. We conclude that several aspects of the D. salina recovery from photoinhibition are light independent.

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Responses of Detached Rice Leaves (Oryza sativa L.) To Moderate Supplementary Ultraviolet-B Radiation Allow Early Screening for Relative Sensitivity to Ultraviolet-B Irradiation

Functional Plant Biology ◽

10.1071/pp9930285 ◽

1993 ◽

Vol 20 (3) ◽

pp. 285 ◽

Cited By ~ 12

Author(s):

LK Huang ◽

J He ◽

WS Chow ◽

MI Whitecross ◽

JM Anderson

Keyword(s):

Oryza Sativa L ◽

Relative Sensitivity ◽

Ultraviolet B ◽

Total Soluble Protein ◽

Rice Cultivars ◽

Short Term ◽

Early Screening ◽

Short Term Treatment ◽

Detached Leaves ◽

Rice Leaves

Responses to short-term supplementary ultraviolet-B (UV-B) radiation were studied in detached leaves of two indica rice cultivars (Er Bai Ai and Lemont) to evaluate whether this might be an initial method for screening for UV-B susceptibility. Leaf tissue from plants grown in a greenhouse (28�C day/ 20�C night, with a maximum irradiance of 800-1000 μmol photons m-2 s-1) was placed under moderate supplementary UV-B radiation for 20 h. The effects of this short-term treatment were measured by determining the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm), quantum yield of photosynthetic O2 exchange, chlorophyll content, maximum Rubisco activity as well as the concentrations of total soluble protein and Rubisco protein. All the above parameters showed considerable declines, which were always greater in cv. Er Bai Ai than in cv. Lemont. The in vivo activation of Rubisco was markedly increased in detached leaves treated with supplementary UV-B compared with control leaves; the increase was greater in cv. Er Bai Ai than in cv. Lemont. The photosynthetic responses invoked in the detached rice leaves are remarkably similar to those observed previously [He et al. (1993). Aust. J. Plant Physiol. 20, 129-42] in intact rice plants which had a longer-term supplementary UV-B exposure of comparable cumulative biologically effective UV-B dosage. We conclude that rapid short-term responses of detached leaves allow early screening of relative sensitivity of rice cultivars to UV-B.

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