Phloem sap intricacy and interplay with aphid feeding

Aphididae feed upon the plant sieve elements (SE), where they ingest sugars, nitrogen compounds and other nutrients. For ingestion, aphid stylets penetrate SE, and because of the high hydrostatic pressure in SE, phloem sap exudes out into the stylets. Severing stylets to sample phloem exudates (i.e. stylectomy) has been used extensively for the study of phloem contents. Alternative sampling techniques are spontaneous exudation upon wounding that only works in a few plant species, and the popular EDTA-facilitated exudation technique. These approaches have allowed fundamental advances on the understanding of phloem sap composition and sieve tube physiology, which are surveyed in this review. A more complete picture of metabolites, ions, proteins and RNAs present in phloem sap is now available, which has provided large evidence for the phloem role as a signalling network in addition to its primary role in partitioning of photo-assimilates. Thus, phloem sap sampling methods can have remarkable applications to analyse plant nutrition, physiology and defence responses. Since aphid behaviour is suspected to be affected by phloem sap quality, attempts to manipulate phloem sap content were recently undertaken based on deregulation in mutant plants of genes controlling amino acid or sugar content of phloem sap. This opens up new strategies to control aphid settlement on a plant host

Composition biochimique de la sève phloémienne de la luzerne et performances du puceron du pois : effet d'un déficit hydrique

National audienc

Analyse fonctionnelle de l'impact d'Acyrthosiphon pisum sur la luzerne Medicago Sativa : objectif, cadre, exemple.

National audienc

Composition en sucres et en acides amines de la seve phloemienne de la luzerne (Medicago sativa L.) : effets de facteurs ecophysiologiques et consequences sur les relations luzerne/puceron du pois (Acyrthosiphon pisum Harris)

Diplôme : Dr. d'Universit

Effects of controlled densities and locations of pea aphid populations on stem elongation rate of alfalfa

International audienc

Heat shock exposure during early wheat grain development can reduce maximum endosperm cell number but not necessarily final grain dry mass.

Post-anthesis heat shocks, which are expected to increase in frequency under climate change, may affect wheat grain development and lead to significant decreases in grain yield. Grain development occurs in three phases, the lag-phase, the filling-phase, and maturation. The growth of the three main compartments of the grain (outer layers (OLs), endosperm, embryo) is staggered, so that heat shocks affect time- and tissue-specific growth processes differentially depending on their timing. We hypothesized that heat shocks during the lag-phase may reduce final grain size, resulting from a reduction in endosperm cell number and/or a restricted OLs growth. Plants were heated for four consecutive days during the lag-phase or the filling-phase or both phases (lag- and filling-). Heat shocks consisted in four hours a day at 38°C and 21°C for the rest of the day. Controlled plants were maintained at 21/14°C (day/night). For each temperature treatment, kinetics of whole grain and compartment masses and dimensions were measured as well as the endosperm cell number. An early heat shock reduced endosperm cell proliferation. However, the growth patterns neither of endosperm nor of OLs were modified compared to controls, resulting in no differences in final grain size. Furthermore, compared to controls, a single heat shock during the filling-phase reduced both the duration and rate of dry mass accumulation into grains, whereas two consecutive shocks reduced the duration but enhanced the rate of dry mass of accumulation, even when endosperm cell number was reduced. The mean endosperm cell size was shown to be larger after early heat shocks. All together, these results suggest a compensatory mechanism exists to regulate endosperm cell size and number. This process might be a new mechanistic target for molecular studies and would improve our understanding of post-anthesis wheat tolerance to heat-shocks

Final masses and dimensions of basal mature grains from the central spikelets of wheat plants exposed to heat shocks.

Final masses and dimensions of basal mature grains from the central spikelets of wheat plants exposed to heat shocks.</p

Masses and dimensions of basal grains from the central spikelets at the end of the lag-phase.

Masses and dimensions of basal grains from the central spikelets at the end of the lag-phase.</p

Mean daily grain temperature (m ± SD, n = 4) over the two heat shock treatment periods (four consecutive days during lag-phase and/or filling phase of grain growth).

The required mean daily air temperature was 18.5°C and 23.8°C under Control and heat shock treatments respectively. (DOCX)</p

Relationship between the maximum endosperm cells and the final grain dry mass (A) and endosperm dry mass (B).

For each heat shock treatment, each point corresponds to the estimated mean value by the fitting of growth functions to the observed values (3-parms logistic and Gompertz with maxima for dry mass and endosperm cell number, respectively (S1 Table)). Heat shocks (HS) were applied during the lag-phase (HS1), during the grain filling-phase (HS2) or during both the lag-phase and filling-phase (HS12) of the grain development, compared to Control. (TIF)</p