Overexpression of Hevea brasiliensis ethylene response factor HbERF‐IXc5 enhances growth and tolerance to abiotic stress and affects laticifer differentiation

Ethylene response factor 1 (ERF1) is an essential integrator of the jasmonate and ethylene signalling pathways coordinating a large number of genes involved in plant defences. Its orthologue in Hevea brasiliensis, HbERF‐IXc5, has been assumed to play a major role in laticifer metabolism and tolerance to harvesting stress for better latex production. This study sets out to establish and characterize rubber transgenic lines overexpressing HbERF‐IXc5. Overexpression of HbERF‐IXc5 dramatically enhanced plant growth and enabled plants to maintain some ecophysiological parameters in response to abiotic stress such as water deficit, cold and salt treatments. This study revealed that HbERF‐IXc5 has rubber‐specific functions compared to Arabidopsis ERF1 as transgenic plants overexpressing HbERF‐IXc5 accumulated more starch and differentiated more latex cells at the histological level. The role of HbERF‐IXc5 in driving the expression of some target genes involved in laticifer differentiation is discussed.     

Experimental tests of the mechanism for ant-enhanced growth in an ant-tended lycaenid butterfly

In a previous laboratory study, larvae of the ant-tended lycaenid butterfly Hemiargus isola developed into larger adults when reared with the ant Formica perpilosa than when reared without ants. Ants neither fed butterfly larvae nor significantly delayed developmental duration. We investigated two non-exclusive hypotheses for the mechanism of this effect: larvae tended by F. perpilosa (1) consume more food, and (2) digest the food they consume more efficiently, than those reared without ants. Larvae reared in the laboratory with F. perpilosa ants became significantly heavier adults but produced a significantly lighter fecal mass than their untended counterparts, suggesting that greater food consumption was not the primary mechanism for the higher growth rates of ant-tended larvae. Tended and untended larvae were equally proficient at digesting the contents of pollen (a major natural food source) throughout the tended portion of the life cycle. Taken together, the results suggest that neither greater consumption nor higher assimilation accounts for the larger size of F. perpilosa-tended larvae. We propose that tended larvae may expend less energy than their untended counterparts. Received: 3 January 1997 / Accepted: 18 June 1997     

Natural Senescence of Pea Leaves (An Activated Oxygen-Mediated Function for Peroxisomes)

We studied the activated oxygen metabolism of peroxisomes in naturally and dark-induced senescent leaves of pea (Pisum sativum L.). Peroxisomes were purified from three different types of senescent leaves and the activities of different peroxisomal and glyoxysomal enzymes were measured. The activities of the O2-- and H2O2-producing enzymes were enhanced by natural senescence. Senescence also produced an increase in the generation of active oxygen species (O2- and H2O2) in leaf peroxisomes and in the activities of two glyoxylate-cycle marker enzymes. A new fraction of peroxisomes was detected at an advanced stage of dark-induced senescence. Electron microscopy revealed that this new peroxisomal fraction varied in size and electron density. During senescence, the constitutive Mn-superoxide dismutase (SOD) activity of peroxisomes increased and two new CuZn-SODs were induced, one of which cross-reacted with an antibody against glyoxysomal CuZn- SOD. This fact and the presence of glyoxylate-cycle enzymes support the idea that foliar senescence is associated with the transition of peroxisomes into glyoxysomes. Our results indicate that natural senescence causes the same changes in peroxisome-activated oxygen metabolism as dark-induced senescence, and reinforce the hypothesis of an effective role of peroxisomes and their activated oxygen metabolism in this stage of the life cycle.     

Assessing changes in the genetic diversity of potato gene banks. 1. Effects of seed increase

 Effects of gene bank seed-increases on the genetic integrity of potato germ plasm is a major concern of gene bank managers. Thus the Association of Potato Inter-gene-bank Collaborators (APIC), a consortium of world potato gene bank leaders, initiated this joint research project using RAPD markers to determine genetic relationships between increased generations within accessions. Solanum jamesii (2n=2x=24) and S. fendleri (2n=4x=48), two wild potato species native to North America, were used as plant material. These species represented two major breeding systems found among Solanum species: outcrossing diploids and inbreeding disomic tetraploids, respectively. Comparisons were made between populations one generation apart and between sister populations generated from a common source. Fourteen such comparisons within S. jamesii accessions had an average similarity of 96.3%, and 21 such comparisons within S. fendleri accessions had an average similarity of 96.0%. No pairs of populations were significantly different, despite the fact that RAPD markers easily separated all of these very similar accessions within their respective species. Only one of six S. jamesii accessions analyzed showed a significant change in gene frequencies among generations. These findings indicate that there has been minimal loss or change of genetic diversity in ex situ germplasm using the gene bank techniques standard at NRSP-6 and other world potato gene banks. Received: 28 October 1996 / Accepted: 7 March 1997     

Phenology of a dioecious population of Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in a stream from southeastern Brazil

The seasonal dynamics of a dioecious population of Batrachospermum delicatulum (Skuja) Necchi and Entwisle was evaluated biweekly during the growth period of the macroscopic gametophyte, from late autumn (May) to early spring (October) in a third-order stream from the northeast region of Sao Paulo State, southeastern Brazil (20?43'S, 49?13'W). The population fluctuated throughout the study period in terms of percentage cover, frequency and chlorophyll content. Percent cover and frequency showed a clear pattern with the lowest values at the initial and final stages of the growth period and the highest in July-August (winter). Gametophyte growth was associated with high illumination and low temperature, which agrees with most observations on Batrachospermales in stream environments. Relatively wide variations in reproductive characteristics were observed during the growth period, which were not correlated with percentage cover, frequency and chlorophyll content. The phenologic pattern observed in this population was characterized by a synchronic development of female/male plant ratio with the number of spermatangia per plant resulting in: (i) a higher proportion of fertilized (carpo-sporophytic) plants associated with more male plants; (ii) higher fertilization rates during the periods with higher production of spermatangia per plant; and (iii) higher production of spermatangia per plant when the population had more male plants. These characteristics were largely associated with water temperature and ion content. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the relatively low proportion of male to female plants and high fertilization rates. These data are consistent with a hypothesis to explain high fertilization rates in dioecious species in lotic habitats consisting of outcrossing among adjacent plants with intermingled male and female branches within an algal cluster. Efficient reproductive strategies have been reported in dioecious, monoecious and even mixed populations of B. delicatulum and can be interpreted as adaptations to successfully colonize streams with different characteristics.     

Hypoxic metabolic response of the golden-mantled ground squirrel.

We examined the magnitude of the hypoxic metabolic response in golden-mantled ground squirrels to determine whether the shift in thermoregulatory set point (T(set)) and subsequent fall in body temperature (T(b)) and metabolic rate observed in small mammals were greater in a species that routinely experiences hypoxic burrows and hibernates. We measured the effects of changing ambient temperature (T(a); 6--29 degrees C) on metabolism (O(2) consumption and CO(2) production), T(b), ventilation, and heart rate in normoxia and hypoxia (7% O(2)). The magnitude of the hypoxia-induced falls in T(b) and metabolism of the squirrels was larger than that of other rodents. Metabolic rate was not simply suppressed but was regulated to assist the initial fall in T(b) and then acted to slow this fall and stabilize T(b) at a new, lower level. When T(a) was reduced during 7% O(2), animals were able to maintain or elevate their metabolic rates, suggesting that O(2) was not limiting. The slope of the relationship between temperature-corrected O(2) consumption and T(a) extrapolated to a T(set) in hypoxia equals the actual T(b). The data suggest that T(set) was proportionately related to T(a) in hypoxia and that there was a shift from increasing ventilation to increasing O(2) extraction as the primary strategy employed to meet increasing metabolic demands under hypoxia. The animals were neither hypothermic nor hypometabolic, as T(b) and metabolic rate appeared to be tightly regulated at new but lower levels as a result of a coordinated hypoxic metabolic response.