65 research outputs found
Transient winter leaf reddening in Cistus creticus characterizes weak (stress-sensitive) individuals, yet anthocyanins cannot alleviate the adverse effects on photosynthesis
Under apparently similar field conditions individual plants of Cistus creticus turn transiently red during winter, while neighbouring plants remain green. These two phenotypes provide a suitable system for comparing basic photosynthetic parameters and assessing critically two hypotheses, i.e. anthocyanins afford photoprotection and anthocyanins induce shade characteristics on otherwise exposed leaves. With that aim, pigment levels and in vivo chlorophyll fluorescence parameters were monitored in dark-acclimated (JIP-test) and light-acclimated (saturation pulse method) leaves during both the green and the red period of the year. No evidence for actual photoprotection by anthocyanins was obtained. On the contrary, all fluorescence parameters related to yields and probabilities of photochemical energy conversion and electron flow, from initial light trapping to final reduction of ultimate electron acceptors in PSI, declined in the red phenotype after leaf reddening. Moreover, the pool sizes of final electron acceptors of PSII diminished, indicating that both photosystems were negatively affected. Vulnerability to winter stress was also indicated by sustained chlorophyll loss, inability to increase the levels of photoprotective xanthophylls and increased quantum yield of non-regulated energy loss during reddening. However, during the same period, the relative PSII antenna size increased, indicating an apparent shade acclimation after anthocyanin accumulation, while changes in the photosynthetic pigment ratios were also compatible to the shade acclimation hypothesis. All parameters recovered to pre-reddening values upon re-greening. It is concluded that the photosynthetic machinery of the red leaf phenotype has an inherently low capacity for winter stress tolerance, which is not alleviated by anthocyanin accumulation
Visual ecology of aphids – a critical review on the role of colours in host finding
We review the rich literature on behavioural responses of aphids (Hemiptera: Aphididae) to stimuli of different colours. Only in one species there are adequate physiological data on spectral sensitivity to explain behaviour crisply in mechanistic terms.
Because of the great interest in aphid responses to coloured targets from an evolutionary, ecological and applied perspective, there is a substantial need to expand these studies to more species of aphids, and to quantify spectral properties of stimuli rigorously. We show that aphid responses to colours, at least for some species, are likely based on a specific colour opponency mechanism, with positive input from the green domain of the spectrum and negative input from the blue and/or UV region.
We further demonstrate that the usual yellow preference of aphids encountered in field experiments is not a true colour preference but involves additional brightness effects. We discuss the implications for agriculture and sensory ecology, with special respect to the recent debate on autumn leaf colouration. We illustrate that recent evolutionary theories concerning aphid–tree interactions imply far-reaching assumptions on aphid responses to colours
that are not likely to hold. Finally we also discuss the
implications for developing and optimising strategies
of aphid control and monitoring
Leaf anatomy of Qualea parviflora (Vochysiaceae) in three phytophysiognomies of the Mato Grosso State, Brazil
Identification of differentially expressed genes implicated in peel color (red and green) of Dimocarpus confinis
Allelopathic and Water Conserving Functions of Leaf Epicuticular Exudates in the Mediterranean Shrub Dittrichia viscosa
Organic Cosolutes as Stabilizers of Phosphoenolpyruvate Carboxylase in Storage: an Interpretation of Their Action
Organic Cosolutes Increase the Catalytic Efficiency of Phosphoenolpyruvate Carboxylase, From Cynodon Dactylon (L.) Pers., Apparently Through Self-Association of the Enzymic Protein
Seasonal fluctuations in the concentration of UV-absorbing compounds in the leaves of some Mediterranean plants under field conditions
Leaves of 14 representative Mediterranean plant species were collected
on a monthly basis and assayed for UV-absorbing compounds concentration,
either on an area or a dry mass basis, from 1995 to 1997, Strong
seasonal fluctuations were observed in eight species tall evergreens,
two phrygana, one deciduous, one summer perennial and one winter
perennial). Two different patterns of changing concentrations of
UV-absorbing compounds were observed. In the first, concentration of
these compounds was higher in young developing leaves and concentration
declined during maturation, whereas in other plants, the opposite trend
was observed. These differences could be attributed to the particular
leaf surface morphology of each plant. The observed seasonal
fluctuations of UV-absorbing compounds seem to be more correlated to
developmental processes, than to seasonal fluctuations of the naturally
occurring UV-B radiation. Most of the winter perennials did not show
strong fluctuations during the period of development. The concentration
of these compounds varied not only on a seasonal basis among the
examined plants, but between different life forms as well: during
winter, examination of the leaves of 13 species showed that evergreen
sclerophylls and phrygana had at least two-fold higher concentration of
UV-B-absorbing compounds on a leaf area basis than winter perennials. In
addition, during the same season and irrespective of life form and
species, the absorbance at 300 nm per unit of mature leaf area followed
an asymptotic exponential decrease when specific leaf area increased.
The UV-B radiation screening capacity of the leaves of these plants is
discussed in relation to each adaptive strategy
Differential effects of enhanced UV-B radiation on reproductive effort in two chemotypes of Mentha spicata under field conditions
Re-Evaluation of the Effects of Glucose-6-Phosphate and Malate on the Catalytic Properties of Phosphoenolpyruvate Carboxylase From Cynodon dactylon Under Physiological Assay Conditions
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