Plants can perceive a wide range of biotic attackers and respond with targeted induced defenses. Specificity in plant non-selfrecognition occurs either directly by perception of pest-derived elicitors or indirectly through resistance protein recognition of host targets that are inappropriately proteolyzed. Indirect plant perception can occur during interactions with pathogens, yet evidence for analogous events mediating the detection of insect herbivores remains elusive. Here we report indirect perception of herbivory in cowpea (Vigna unguiculata) plants attacked by fall armyworm (Spodoptera frugiperda) larvae. We isolated and identified a disulfide-bridged peptide ( ؉ ICDINGVCVDA ؊ ), termed inceptin, from S. frugiperda larval oral secretions that promotes cowpea ethylene production at 1 fmol leaf ؊1 and triggers increases in the defenserelated phytohormones salicylic acid and jasmonic acid. Inceptins are proteolytic fragments of chloroplastic ATP synthase ␥-subunit regulatory regions that mediate plant perception of herbivory through the induction of volatile, phenylpropanoid, and protease inhibitor defenses. Only S. frugiperda larvae that previously ingested chloroplastic ATP synthase ␥-subunit proteins and produced inceptins significantly induced cowpea defenses after herbivory. Digestive fragments of an ancient and essential plant enzyme, inceptin functions as a potent indirect signal initiating specific plant responses to insect attack.elicitor ͉ guard hypothesis ͉ indirect perception ͉ insect herbivory ͉ plant defense A mechanistic understanding and targeted improvement of plant resistance traits are recognized as essential in combating yield losses from crop pests. Plants can perceive and defensively respond to attack either directly by impeding pest growth or indirectly by promoting advantageous interactions with beneficial organisms (1-7). Great progress has been made in the identification of plant receptor-like kinase families mediating perception of biotic attack and the subsequent activation of signal transduction cascades spanning interactions of GTP binding proteins, mitogen-activated protein kinases, phytohormones, transcription factors, and ultimately induced biochemical defenses (2,8). Despite these advances, relatively few candidate elicitors and ligands responsible for the initiation and specificity of induced plant defenses to pest attack have been identified (1, 2). This void is especially acute in the case of insect herbivore perception and is surprising given both the significance of plant-insect interactions in arthropod and angiosperm evolution and the role of insects in facilitating plant pathogen entry (9, 10).Induced plant defenses are initiated in part by the direct perception of elicitors derived from offending organisms. For example, maize (Zea mays) and tobacco (Nicotiana attenuata) perceive insect attack through the direct detection of fatty acid amino acid conjugate (FAC) elicitors present in insect oral secretions (OS). Plants respond with indirect defenses in the form of indu...
A model for the turnover of organic matter in soil, ROTHC‐26.3, can be used to calculate how much organic C needs to enter a soil annually in order to maintain a specified stock of soil organic C. The annual return of organic C thus calculated, plus the amount of organic C removed annually from the site by harvesting, burning, etc., provides an estimate of the Net Primary Production (NPP) of that site, averaged over many years. The new method was used to calculate NPP for two adjacent savanna sites in the Nairobi National Park in Kenya, one grazed and one not, and for a dry Miombo woodland site in Zambia. Both the Kenyan and Zambian sites are taken to be at equilibrium, with soil organic C levels at steady state. Soils from the three sites were analyzed by layer for organic C, δ14C, δ13C, soil microbial biomass C, total N, pH, and clay content. Radiocarbon measurements were >100% modern in the surface layers (0–15 cm) of the Kenyan soils (both Vertisols) and in all three layers (0–15, 15–30 and 30–50 cm) of the Zambian soil (an Oxisol), presumably because of 14C coming from the testing of thermonuclear bombs. The 15–30 cm layer of the Kenyan soils dated at ∼500 yr and the 30–50 cm layer at ∼900 yr. The 14C data were consistent with the presence of a small inert fraction of organic C that accounted for an increasing proportion of total organic C with increasing soil depth. The 13C data indicated that the Kenyan soils had developed under C4 vegetation, whereas the Zambian soils had developed under vegetation dominated by C3 plants. From these results the annual input of C to soil from the ungrazed Kenyan site was calculated to be 388 g C·m−2·yr−1, to the grazed site 380 g C·m−2·yr−1, and to the Zambian soil 373 g C·m−2·yr−1. Taking the loss of C from the Kenyan sites by burning to be 40 g C·m−2·yr−1, the mean NPP for both Kenyan sites is 424 g C·m−2·yr−1. This value for NPP is compatible with earlier estimates of NPP by botanical methods from the same site in Kenya. Wood‐taking is thought to be minimal in the protected Zambian woodland, so that here the annual input of C to the soil can be taken as the NPP without great error. This new method provides a long‐term, integrated measure of NPP that should complement and enhance productivity measurements made by harvest methods over shorter periods.
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