Cysteine: A multifaceted amino acid involved in signaling, plant resistance and antifungal development.

Early effects induced by cysteine were monitored using the model of Mimosa pudica pulvinar cells. Rapid dose-dependent membrane depolarization (within seconds) and modification of proton secretion (within minutes) were triggered at cysteine concentrations higher than 0.1 mM.

NaCl - Changes stem morphology, anatomy and phloem structure in Lucerne (Medicago sativa cv. Gabès): Comparison of upper and lower internodes.

In M. sativa cv. Gabès plants treated with 150mM NaCl, the height of the stem is decreased and the internode number, length and diameter are reduced.

Source-to-sink transport of sugar and regulation by environmental factors.

Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors.

Compatible plant-aphid interactions: how aphids manipulate plant responses.

To access phloem sap, aphids have developed a furtive strategy, their stylets progressing towards sieve tubes mainly through the apoplasmic compartment. Aphid feeding requires that they overcome a number of plant responses, ranging from sieve tube occlusion and activation of phytohormone-signalling pathways to expression of anti-insect molecules. In addition to bypassing plant defences, aphids have been shown to affect plant primary metabolism, which could be a strategy to improve phloem sap composition in nutrients required for their growth.

Salicylic acid transport in Ricinus communis involves a pH-dependent carrier system in addition to diffusion.

Despite its important functions in plant physiology and defense, the membrane transport mechanism of salicylic acid (SA) is poorly documented due to the general assumption that SA is taken up by plant cells via the ion trap mechanism. Using Ricinus communis seedlings and modeling tools (ACD LogD and Vega ZZ softwares), we show that phloem accumulation of SA and hydroxylated analogs is completely uncorrelated with the physicochemical parameters suitable for diffusion (number of hydrogen bond donors, polar surface area, and, especially, LogD values at apoplastic pHs and Delta LogD between apoplast and phloem sap pH values). These and other data (such as accumulation in phloem sap of the poorly permeant dissociated form of monohalogen derivatives from apoplast and inhibition of SA transport by the thiol reagent p-chloromercuribenzenesulfonic acid [pCMBS]) lead to the following conclusions.

Magnesium deficiency in sugar beets alters sugar partitioning and phloem loading in young mature leaves.

Magnesium deficiency has been reported to affect plant growth and biomass partitioning between root and shoot. The present work aims to identify how Mg deficiency alters carbon partitioning in sugar beet (Beta vulgaris L.) plants.

Dissection of the effects of the aphid Acyrthosiphon pisum feeding on assimilate partitioning in Medicago sativa.

•  The short-term effects (24 h infestation) of the pea aphid on C-assimilate partitioning and stem elongation rate (SER) of alfalfa were investigated in relation to possible mechanisms (nutrient removal, mechanical or chemical stimuli) involved in the impact of the aphid on plants. •  Different combinations of aphid numbers, developmental stages and location on the stem were tested on both SER and C-assimilate partitioning within the plant overall, and in the various compartments of the growth zone (GZ): apex, apical bud and elongating internodes. •  Stem elongation rate reduction could be related quantitatively to assimilate withdrawal but did not depend on this parameter only.