Can selection to escape nectar thieving force plants to portion nectar in many flowers?

There are several hypotheses which try to explain why particular plants produce just the number of flowers that they do. These hypotheses include: compromises between the attraction of pollinators and avoiding self-pollination by geitonogamy; optimal nectar production as a result of diminishing gains of nectar production; opportunity for selective abortion; or different bet-hedging strategies. In this paper, I present a hypothesis which interferes with the others concerning flower numbers in plants: nectar thieving can apply a selection force in plants which result in a portioning of nectar in many flowers. Energy saved by reducing the quantity of nectar in each flower can be directed into greater flower numbers.     

Is hexokinase really a sugar sensor in plants?

The molecular mechanisms by which plant cells sense sugar levels are not understood, but current models (adapted from models for sugar sensing in yeast) favour hexokinase as the primary sugar sensor. However, the hypothesis that yeast hexokinase has a signalling function has not been supported by more recent studies and the idea that hexokinase is involved in sugar sensing in plants has yet to be proven.     

Do NK cells regulate human autoimmunity?

Natural killer cells have been shown to regulate autoimmune responses under experimental conditions in animals. However, a similar role for human NK cells has not been investigated, although NK cells constitute a significant fraction of the infiltrating cells in a range of autoimmune diseases. This review investigates the evidence, both theoretical and experimental, for the involvement of these cells in human immunopathology.     

Do transgenic plants affect rhizobacteria populations?

Plant genetic manipulation has led to the development of genetically modified plants (GMPs) expressing various traits. Since their first commercial use in 1996, GMPs have been increasingly used, reaching a global cultivating production area of 114.3 million hectares in 2007. The rapid development of agricultural biotechnology and release of GMPs have provided many agronomic and economic benefits, but has also raised concerns over the potential impact these plants might have on the environment. Among these environmental concerns, the unintentional impact that GMPs might have on soil‐associated microbes, especially rhizosphere‐inhabiting bacteria or rhizobacteria, represents one of the least studied and understood areas. As rhizobacteria are responsible for numerous key functions including nutrient cycling and decomposition, they have been defined as good indicator organisms to assess the general impact that GMPs might have on the soil environment. This minireview summarizes the results of various experiments that have been conducted to date on the impact of GMPs on rhizobacteria. Both biological and technical parameters are discussed and an attempt is made to determine if specific rhizobacterial responses exist for the different categories of GMPs developed to date.     

Do plants ever compete for space?

The term “competition for space” occurs often in ecological literature, but there has never been a direct demonstration of this competition. In fact it has been shown that plant canopies are mainly empty of plant organs. F.E. Clements recognized this. He suggested that one of the few situations in which competition for space would occur was in an unthinned row of radishes. Even this has never been demonstrated. We sowed radishes (Raphanus sativa) in a dense row and let them grow to maximum size in favourable conditions. For comparison, the same number of radish seeds were sown in a double, offset row. Squeezing the radish plants into one row was largely compensated by sideways movement of their hypocotyl/taproots, but total plant mass was reduced by 7.5%. Even this cannot be definitely attributed to competition for space. We conclude that competition for space, if it exists at all, is only a small effect even in conditions very favourable for it. It can, as Clements said, be ignored for natural communities.     

Do prostaglandins regulate external gill regression in anurans?

Although the endocrinological mechanism controlling regression of the internal, larval gills of anurans (frogs and toads) is well understood, the mechanism regulating loss of the external, embryonic gills is not known. Based on the homology of the mammalian ductus arteriosus with a portion of the amphibian branchial arches, and the regulation of blood flow in the mammalian ductus by prostaglandins of the E family (PGEs), we hypothesized that anuran external gill loss is also regulated by PGEs. To test this hypothesis, we topically applied both PGE2 and a synthetic analogue of PGE1, misoprostol, to embryos and young hatchlings of the red-eyed treefrog, Agalychnis callidryas. Both agents accelerated external gill regression. Furthermore, misoprostol overrode the inhibitory effect of hypoxia on gill regression in hatchlings and induced rapid loss of external gills in embryos, which normally maintain the gills until hatching. These observations support the hypothesis that PGEs regulate anuran external gill loss. The specific site of action for prostaglandins within the gills is not known; however, PGEs are secreted in the oral mucus of tadpoles, and this could be a natural topical source for these agents. PGEs offer a tool for manipulation of external gills and should facilitate tests of the physiological importance of these structures.     

Do memory processes occur also in plants?

Plantlets of Bidens pilosus L. remembered a symmetry-breaking signal (the puncturing of one of the cotyledons), but expressed it only after being made permissive (by removing the apex). The mean value of the memorization index was 0.52. There was a labile short-term and a well-fixed long-term memory. The memorization process was dependent on the number of stimuli, and on the mineral status of the plant.     

Do tomato plants contain endogenous indoleacetylaspartic acid?

The data of Rowet al. (1961) on endogenous indoleacetylaspartic acid in tomato plants were reexamined. It was shown that two indole compounds were present in ethanolic extract of tomato stems and leaves. The predominating substance was concluded to be N-malonyltryptophan on account of its UV- and IR-spectra, colour reactions with the Ehrlich and Salkovski reagents and products of acidic and alkaline hydrolyses. The chemical nature of the second indole compound remained unknown. It differed from N-malonyltryptophan, N-aeetyltryptophan, indoleacetylaspartic acid and indoleacetic acid and may result from non-enzymatic transformation of N-malonyltryptophan.     

Is trehalose-6-phosphate a regulator of sugar metabolism in plants?

It has recently emerged that many higher plants can synthesize trace amounts of trehalose. In arabidopsis disruption of the first step of trehalose synthesis, catalysed by trehalose-6-phosphate synthase (TPS), has lethal consequences, demonstrating an important physiological role. It is not yet clear what the precise function of trehalose synthesis is, but there is mounting evidence that trehalose-6-phosphate is implicated in the regulation of sugar metabolism. Further work is necessary to confirm this hypothesis and determine the underlying mechanism.     

Drought perception by plants Do cells of droughted plants experience water stress?

Because of regulations at the whole-plant level, cells of droughted plants do not necessarily experience dehydration. In fact, recent data suggest that they usually do not in the range of water deficits compatible with agriculture. In this range, leaf water potential and cell turgor are frequently maintained at high values in spite of decreasing soil water status. As a consequence, water stress cannot be defined by plant water status, except when very rapid and severe water deficits cause catastrophic events such as xylem embolism or severe cell dehydration. In water deficits compatible with agricultural situations, plant water status is in many cases tightly controlled by the plant. Water stress should then be defined by water statuses at plant boundaries, i.e. soil and air. Partial maintenance of plant water status under water deficit is allowed by controls of stomatal conductance, root and leaf expansions and leaf senescence. These processes involve both chemical and hydraulic signallings from roots. All these controls tend to reduce transpiration (stomatal closure, reduced leaf growth or leaf senescence) or to increase water uptake (maintenance of root growth or increase in root/shoot ratio). During relatively mild stresses, the role of abscisic acid, frequently considered as a stress hormone, in fact appears to be to avoid dehydration at the cellular level. In the cases described here, selecting plants for better resistance to cell dehydration may not be the best strategy for improving drought resistance of crops.     

Do caveolins regulate cells by actions outside of caveolae?

Caveolae (caveolin-containing lipid rafts) are plasma membrane domains that scaffold and organize a variety of important proteins in eukaryotic cells. Recent work shows that caveolins can act independently of caveolae, both in cells that lack caveolae (e.g. neurons and leukocytes) and in non-caveolar regions of cells that have caveolae (e.g. cardiac myocytes and fibroblasts). Phosphorylation of caveolins can influence the scaffolding of protein partners, and caveolins appear to participate in the protection and trafficking of proteins to and from the plasma membrane. Together, these results suggest that, despite their name, caveolins should now be thought of as proteins that scaffold signaling and other proteins in both caveolar and non-caveolar regions.