Chlamydomonas raudensis(UWO 241), Chlorophyceae, exhibits the capacity for rapid D1 repair in response to chronic photoinhibition at low temperature1

To analyse characteristic patterns of dynamic and chronic photoinhibition within a plant community, a new technique is proposed, which is based on the long- and short-term recovery time of maximum photochemical efficiency of PSII (F v/F m) after environmental stress. Chronic photoinhibition was determined as a sustainable decrease in predawn F v/F m, occurring during periods of prolonged stress, whereas dynamic photoinhibition was assessed from the fully reversible diurnal decline in F v/F m. Applied to a Mediterranean macchia ecosystem, this definition allowed the characterization of typical annual patterns of chronic and dynamic photoinhibition. Both types of photoinhibition were highest during summer drought. However, differences emerged among the ten dominant macchia species regarding their susceptibility to chronic photoinhibition during different seasons. Chronic and dynamic photoinhibition were dependent on leaf orientation. Semi-deciduous species avoided enhanced chronic photoinhibition through a reduction of excessive light interception by vertical foliage orientation during summer, whereas evergreen sclerophylls did not exhibit pronounced structural photoprotective mechanisms. Chronic and total photoinhibition were significantly correlated with predawn and midday water potentials, respectively, and a grouping of the macchia species into three functional groups is proposed according to this relationship.

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Comparative stomatal conductance and chlorophyll a fluorescence in leaves vs. fruits of the cerrado legume tree, Dalbergia miscolobium

Brazilian Journal of Plant Physiology ◽

10.1590/s1677-04202004000200004 ◽

2004 ◽

Vol 16 (2) ◽

pp. 89-93 ◽

Cited By ~ 7

Author(s):

José Pires de Lemos Filho ◽

Rosy Mary dos Santos Isaias

Keyword(s):

Water Vapor ◽

Stomatal Conductance ◽

Quantum Yield ◽

Chlorophyll A ◽

Chlorophyll A Fluorescence ◽

Electron Transport Rate ◽

Early Morning ◽

Effective Quantum Yield ◽

Quantum Yield Of Psii ◽

Chronic Photoinhibition

The aim of this study was to compare water vapor conductance and chlorophyll a fluorescence between leaflets and fruits of Dalbergia miscolobium, the Jacaranda tree. The frequency of stomata on the leaflets was 20 times higher than that observed on the fruits, and this was related with the lower conductance of the fruits in comparison with the leaflets. The potential quantum yield of PSII (Fv /Fmax) was significantly lower in fruits than in leaflets. The Fv /Fmax values for leaflets increased to over 0.8 during the afternoon, indicating the occurrence of dynamic photoinhibition. In contrast, Fv /Fmax values for fruits remained low even at early morning, indicating the occurrence of chronic photoinhibition. The maximum values of effective quantum yield (deltaF/F'm), and of the apparent electron transport rate (ETRmax) were higher in leaflets than in fruits. It was concluded that, like other green tissues, the pericarp of D. miscolobium was photosynthetically active, and therefore can contribute to the maintenance of the fruits and/or to the development of the seeds.

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