Control of systemically induced herbivore resistance by plant vascular architecture

Patterns of systemically induced resistance (SIR) in Eastern Cottonwood, Populus deltoides, measured by reduced feeding of the leaf-chewing beetle, Plagiodera versicolora, were shown to be directly related to the distribution of the plant vasculature. Mechanical damage to single leaves resulted in SIR in non-adjacent, orthostichous leaves (vertically aligned on the stem) with direct vascular connections, both up and down the shoot; but no SIR in adjacent, non-orthostichous leaves with less direct vascular connections. The control that the plant vasculature exerts over signal distribution following wounding can therefore be used to predict SIR patterns, explain variation in the distribution of SIR, and relate this ecologically important phenomenon to biochemical processes of systemic gene expression and biochemical resistance mechanisms.     

A Stochastic Model For Cell Populations With Circadian Rhythms

A mathematical model for cell kinetics, based on a random walk, is developed. the model allows variations with time of the rates of passage of proliferating cells through the four phases of the mitotic cycle. Circadian variations in the mitotic and labelling indices of the Syrian hamster cheek pouch epithelium have previously been observed, and the random walk model has been used to simulate this phenomenon. Assuming that all basal cells are proliferative and that these cells leave the basal layer randomly throughout the mitotic cycle to become differentiated cells, it was found that the experimentally observed circadian rhythms of the mitotic and labelling indices could be reproduced in the model by postulating a circadian rhythm in the rate of passage of cells through the G₁ and S phases only. Moreover, the growth activity of cells in both the G₁ and S phases appears to reach a peak during the dark hours of the light-dark cycle, and to fall off rapidly in the early hours of daylight. the postulate of Møller, Larsen & Faber (1974) that injection of the animals with tritiated thymidine causes a shortening of the G₂ phase duration has been qualitatively confirmed by using the random walk model to simulate the FLM and MI curves after injection with tritiated thymidine.     

Analysis of stylar self-incompatibility competence by use of heat induced inactivation

Summary Immersion of Lilium longiflorum pistils in 49 °C water for increasing durations of 1,2,3, or 4 minutes immediately prior to incompatible pollination resulted in a correspondingly progressive decrease in the stylar self-incompatibility competence, as determined from the lengths attained by pollen tubes during 48 hours growth in the styles at 24 °C. Neither pistils remaining on the plant nor those detached from the plant which were immersed after anthesis in 49 °C water for 5 minutes regained self-incompatibility competence during a 48 hour incubation at 24 °C prior to incompatible pollination. Heat treatment of detached pistils as early as 39 hours prior to bud anthesis also resulted in an inactivation of stylar self-incompatibility competence when incompatible pollination was made at 24 hours after anthesis. Experiments utilizing heat treatment of partial lengths of detached whole styles revealed that pollen tubes which have grown through as much at 45 millimeters of either a physiologically incompatible or compatible portion of the style are still capable of shifting to either a higher growth rate or lower growth rate upon entry into respectively either a physiologically compatible or incompatible portion of the style.     

Age-related changes in in vitro immunoglobulin secretion: Comparison of responses to T-dependent and T-independent polyclonal activators

In vitro Ig secretion by peripheral blood mononuclear cells (MNCs) from old and young donors, in response to T-dependent (TD) [pokeweed mitogen (PWM)] and T-independent (TI) [Salmonella paratyphii B (SPB)] activation were compared. In older donors, the IgG and IgA responses to PWM were comparable to those of young donors; the IgM response was reduced in the elderly. With SPB activation, IgA response was again preserved, whereas IgG response was reduced and IgM secretion was markedly decreased. These data indicate class-specific changes in Ig responsiveness to both TD and TI cell activators with age. The reduction in TI-induced IgG and IgM responses in the elderly suggest that changes in B cells themselves have occurred. The preservation of the TD IgG response in concert with reduced TI response indicates that a decline in T-suppressor influences over B cells in the elderly coupled with reduced B-cell synthesizing capacity can result in apparent “preservation” of the final Ig response. In keeping with the above postulate, analysis of individual elderly donors' responses indicated that some of the old donors responded to PWM, but not SPB; none of the old donors responded to SPB and not PWM. In contrast, some young donors did respond to SPB, but not PWM. These results also suggest that nonresponse to PWM in young donors relates to an override of functionally intact B cells by T-regulator influences.