The occurrence and significance of amino acids in floral nectar

Approximately 1 500 angiosperm species, in previous papers, have been sampled for the assessment of the amino acids (a. a.) in their nectar. We reaffirm that the findings provide statistically significant data linking differences in the concentration with pollinator type. Flowers that are pollinated by animals that have alternative sources of protein-building a. a.’s show lower a. a. concentration than those that are not. There is a tendency for woody plant nectar a. a.’s to be less concentrated than those of herbaceous plants, but there can be “phylogenetic constraints” which may reduce the correlations of a. a. concentration with pollinator type and with life form. The individual a. a.’s form complements which are qualitatively extremely constant within species. Proline is a normal constituent of many nectars and does not necessarily indicate contamination of the nectar by pollen. Criticism of our findings byGottsberger & al. (1984) is answered by reference to our previous publications and those of other workers, and to the presentation of data from California native species, not published previously. All previous postulates are borne out by these new data with the exception of positive correlations of a. a. concentration with “primitive” and “advanced” floral characteristics taken one at a time, which appear to be inconsistent and are affected strongly by the nature of the family in which they occur. Summary data are provided for families and genera which indicate that high or low a. a. concentration can typify certain families and genera of both relatively “primitive” and relatively “advanced” nature. Needs for future research on an ecosystem basis are quoted.     

Pollen-ovule ratios in some Neotropical Araceae and their putative significance

The correlation between pollen-ovule (P/O) ratio and breeding system has generally been analysed with respect either to pollination efficiency, or in terms of sex allocation theory. Pollen/ovule ratios were measured in nine species of Araceae belonging to two genera with bisexual flowers (Anaphyllopsis, Monstera) and three genera with unisexual flowers (Dieffenbachia, Philodendron, Montrichardia). The family Araceae with its unique inflorescence morphology allows the analysis of variations of the P/O ratio with respect to two basal morpho-functional pollination units: the flower or the inflorescence. We found a relationship between the value of the P/O ratio and the breeding system that is partially different from Cruden's results (1977). Some facultative xenogamous species have a higher P/O than the obligatory xenogamous species. A link was found between the P/O and the type of inflorescence, the floral cycle, and the mode of growth.     

The role of free sugars and amino acids in the regulation of biomass partitioning and plant growth

Theoretical plant growth models postulate an important role for growth substrates such as sugars and amino acids. To test this experimentally, spinach plants were grown under controlled conditions and with nitrogen added daily, following different exponential addition schemes. Plants were harvested during exponential growth. Free amino acid levels or free sugar levels were only weakly correlated with growth and biomass partitioning. Factor analysis showed however that the product of free sugar concentration and amino acid concentration yielded a parameter adequately reflecting the plant's nutritional state.It is concluded that growth and biomass partitioning under limiting N conditions cannot be modelled solely based on N substrate levels.     

Taxonomic and functional implications of stigma morphology in species ofCassia,Chamaecrista, andSenna (Leguminosae:Caesalpinioideae)

Two stigma forms occur inChamaecrista andSenna, but only one inCassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.