Mineral nutrient uptake from prey and glandular phosphatase activity as a dual test of carnivory in semi-desert plants with glandular leaves suspected of carnivory
Background and Aims
Ibicella lutea and Proboscidea parviflora are two American semi-desert species of glandular sticky plants that are suspected of carnivory as they can catch small insects. The same characteristics might also hold for two semi-desert plants with glandular sticky leaves from Israel, namely Cleome droserifolia and Hyoscyamus desertorum. The presence of proteases on foliar hairs, either secreted by the plant or commensals, detected using a simple test, has long been considered proof of carnivory. However, this test does not prove whether nutrients are really absorbed from insects by the plant. To determine the extent to which these four species are potentially carnivorous, hair secretion of phosphatases and uptake of N, P, K and Mg from fruit flies as model prey were studied in these species and in Roridula gorgonias and Drosophyllum lusitanicum for comparison. All species examined possess morphological and anatomical adaptations (hairs or emergences secreting sticky substances) to catch and kill small insects.
Methods
The presence of phosphatases on foliar hairs was tested using the enzyme-labelled fluorescence method. Dead fruit flies were applied to glandular sticky leaves of experimental plants and, after 10–15 d, mineral nutrient content in their spent carcasses was compared with initial values in intact flies after mineralization.
Key Results
Phosphatase activity was totally absent on Hyoscyamus foliar hairs, a certain level of activity was usually found in Ibicella, Proboscidea and Cleome, and a strong response was found in Drosophyllum. Roridula exhibited only epidermal activity. However, only Roridula and Drosophyllum took up nutrients (N, P, K and Mg) from applied fruit flies.
Conclusions
Digestion of prey and absorption of their nutrients are the major features of carnivory in plants. Accordingly, Roridula and Drosophyllum appeared to be fully carnivorous; by contrast, all other species examined are non-carnivorous as they did not meet the above criteria.
Abstract
Background and Aims
Ibicella lutea and Proboscidea parviflora are two American semi-desert species of glandular sticky plants that are suspected of carnivory as they can catch small insects. The same characteristics might also hold for two semi-desert plants with glandular sticky leaves from Israel, namely Cleome droserifolia and Hyoscyamus desertorum. The presence of proteases on foliar hairs, either secreted by the plant or commensals, detected using a simple test, has long been considered proof of carnivory. However, this test does not prove whether nutrients are really absorbed from insects by the plant. To determine the extent to which these four species are potentially carnivorous, hair secretion of phosphatases and uptake of N, P, K and Mg from fruit flies as model prey were studied in these species and in Roridula gorgonias and Drosophyllum lusitanicum for comparison. All species examined possess morphological and anatomical adaptations (hairs or emergences secreting sticky substances) to catch and kill small insects.
Methods
The presence of phosphatases on foliar hairs was tested using the enzyme-labelled fluorescence method. Dead fruit flies were applied to glandular sticky leaves of experimental plants and, after 10–15 d, mineral nutrient content in their spent carcasses was compared with initial values in intact flies after mineralization.
Key Results
Phosphatase activity was totally absent on Hyoscyamus foliar hairs, a certain level of activity was usually found in Ibicella, Proboscidea and Cleome, and a strong response was found in Drosophyllum. Roridula exhibited only epidermal activity. However, only Roridula and Drosophyllum took up nutrients (N, P, K and Mg) from applied fruit flies.
Conclusions
Digestion of prey and absorption of their nutrients are the major features of carnivory in plants. Accordingly, Roridula and Drosophyllum appeared to be fully carnivorous; by contrast, all other species examined are non-carnivorous as they did not meet the above criteria.
Data for Roridula and Drosophyllum are taken from Płachno et al. (2006).
Uptake of nutrients from flies as a percentage of control unspent flies (in parentheses) is shown. Statistically significant uptake (positive sign) or release (negative sign) of nutrients (one-way ANOVA): ** P < 0·01, * P < 0·05; n.s., non-significant at P > 0·05; n = 8.
ACKNOWLEDGEMENTS
This paper is dedicated to Professor Jan Jeník, Charles University, Prague, Czech Republic, on the occasion of his 80th birthday, and also to the memory of Dr hab. Andrzej Jankun (1940–2007). Thanks are due to Mrs M. Korchová for providing experimental fruit flies, to Mr K. Pásek for providing plant material, and to Mrs M. Ron, the Director of the Mount Scopus Botanical Gardens at the Hebrew University, Jerusalem, Israel, for providing seeds and valuable advice. Sincere thanks are due to Dr B. Rice and Professor D. W. Darnowski for critically reading of the manuscript and suggested corrections to the English text. This study was partly funded by the Research Project of the Academy of Sciences of the Czech Republic No. AV0Z60050516 and the Jagiellonian University (WRBW, CRBW). B.J.P. received support (Start Programme) via an award from The Foundation for Polish Sciences.