Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima

The relationships between damage-induced electropotential waves (EPWs), sieve tube occlusion, and stop of mass flow were investigated in intact Cucurbita maxima plants. After burning leaf tips, EPWs propagating along the phloem of the main vein were recorded by extra- and intracellular microelectrodes. The respective EPW profiles (a steep hyperpolarization/depolarization peak followed by a prolonged hyperpolarization/depolarization) probably reflect merged action and variation potentials. A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring ∼10 min after burning. Early stop of mass flow, well before completion of callose deposition, pointed to an occlusion mechanism preceding callose deposition. This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids. The early occlusion is probably due to proteins, as indicated by a dramatic drop in soluble sieve element proteins and a simultaneous coagulation of sieve element proteins shortly after the burning stimulus. Mass flow resumed 30–40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities. Stop of mass flow by Ca2+-dependent occlusion mechanisms is attributed to Ca2+ influx during EPW passage; the reversibility of the occlusion is explained by removal of Ca2+ ions

Vacuolar organization in the nodule parenchyma is important for the functioning of pea root nodules

Different models have been proposed to explain the operation of oxygen diffusion barrier in root nodules of leguminous plants. This barrier participates in protection of oxygen-sensitive nitrogenase, the key enzyme in nitrogen fixation, from inactivation. Details concerning structural and biochemical properties of the barrier are still lacking. Here, the properties of pea root nodule cortical cells were examined under normal conditions and after shoot removal. Microscopic observations, including neutral red staining and epifluorescence investigations, showed that the inner and outer nodule parenchyma cells exhibit different patterns of the central vacuole development. In opposition to the inner part, the outer parenchyma cells exhibited vacuolar shrinkage and formed cell wall infoldings. Shoot removal induced vacuolar shrinkage and formation of infoldings in the inner parenchyma and uninfected cells of the symbiotic tissue, as well. It is postulated that cells which possess shrinking vacuoles are sensitive to the external osmotic pressure. The cells can give an additional resistance to oxygen diffusion by release of water to the intercellular spaces

Influence of grain storage practices or kind of structure and pesticide use on insect presence in wheat bulks after a long-term storage: a multi-dimensional analysis

National audienceA survey of stored-wheat bulks in France was carried out during two years in the spring seasons of 2010 and 2011 to improve the knowledge about the relationships between grain storage practices, preventive sanitation, grain insecticidal treatment, stored-grain temperature management, and presence of insect species in grain samples. Ninety-four wheat storage sites were surveyed each year (after 8-9 month storage). Besides the quantitative analysis of grain samples for insect presence and residue content, a questionnaire was submitted to grain-store managers to record their storage practices, the characteristics of their equipment for grain quality preservation, and the preventive and corrective means they use for insect control. The data from these two groups of variables were processed in a multidimensional statistical analysis to reveal significant correlations between grain management practices for sanitary quality maintenance and the level of presence of insects in wheat samples. A strong relation was observed between the kind of storage structure and the frequency of insect presence in wheat samples. Flat storage of large grain bulks was the most risky storage structure vs. vertical storage in metal or concrete bins. A relationship was observed between the frequency of insect presence in samples and stored grain temperature levels and also with the lack of temperature measurement equipment installed inside grain bins linked to cooling aeration systems. Preventive sanitation before the grain harvest period, i.e. systematic cleaning and insecticide spraying of unfilled bins, was related to 50% reduction of insect presence in corresponding grain samples. The preventive chemical treatment of harvested grain before long-term storage was not related to a limitation of insect presence in samples taken after 8-9-month storage period. The results of this representative survey give objective arguments for the implementation of good IPM practices and risk prevention for grain sanitary quality preservation during long-term storage periods

Planning and monitoring of stored malting barley quality maintenance

Representing the stored grain ecosystem for quality maintenance implies therepresentation of all its characteristics that take part in the grain quality degradationprocess. A mixed qualitative and quantitative modelling is used to represent the storedgrain ecosystem. The temperature, moisture content and presence of insects are used ascontrol variables. The quality maintenance operations are represented as actions to beexecuted in time requiring available equipment and consumable. Our planningapproach involves three consecutive stages: treatment to obtain a safe grain storagecondition, storage to maintain the storage condition and dispatch to respond to themarket requirements