Plants naturally cycle amino acids across root cell plasma membranes, and any net efflux is termed exudation. The dominant ecological view is that microorganisms and roots passively compete for amino acids in the soil solution, yet the innate capacity of roots to recover amino acids present in ecologically relevant concentrations is unknown. We find that, in the absence of culturable microorganisms, the influx rates of 16 amino acids (each supplied at 2.5 μ  m) exceed efflux rates by 5% to 545% in roots of alfalfa (Medicago sativa), Medicago truncatula, maize (Zea mays), and wheat (Triticum aestivum). Several microbial products, which are produced by common soil microorganisms such as Pseudomonas bacteria and Fusarium fungi, significantly enhanced the net efflux (i.e. exudation) of amino acids from roots of these four plant species. In alfalfa, treating roots with 200 μ  m phenazine, 2,4-diacetylphloroglucinol, or zearalenone increased total net efflux of 16 amino acids 200% to 2,600% in 3 h. Data from 15N tests suggest that 2,4-diacetylphloroglucinol blocks amino acid uptake, whereas zearalenone enhances efflux. Thus, amino acid exudation under normal conditions is a phenomenon that probably reflects both active manipulation and passive uptake by microorganisms, as well as diffusion and adsorption to soil, all of which help overcome the innate capacity of plant roots to reabsorb amino acids. The importance of identifying potential enhancers of root exudation lies in understanding that such compounds may represent regulatory linkages between the larger soil food web and the internal carbon metabolism of the plant.

Fall dormancy is correlated with improved winter survival in alfalfa (Medicago sativa L.), but the physiological basis for this association is not understood. Our objectives were to determine how selection for contrasting fall dormancy influenced (i) fall height and winter survival, (it) crown bud development, and (iii) sugar, starch, protein concentration and composition of roots and crown buds. Three cycles of selection for contrasting fall dormancy were conducted in Davis, CA using ‘Norseman’, ‘Lahontan’, ‘CUF 101’, and ‘Wadi Qurayat’ as parental sources. Seed of parental cultivars and seed of progeny from the third cycle of selection were planted in rows in the field (Starks‐Fincastle, fine‐silty, mixed, mesic Aerie Ochraqualf) West Lafayette, IN, in May 1993 and 1994, and roots and crown buds were sampled at approximately monthly intervals between September and December. Plant survival was determined in March of the year following seeding. Parental cultivar differences in fall dormancy and winter survival were associated with changes in crown bud development, elevated total nonstructural carbohydrate and sugar concentrations in buds, and sugar and protein accumulation in roots. Cultivar differences in fall dormancy also influenced polypeptide composition of green buds and roots. Selection for greater fall dormancy reduced the height of CUF 101 and markedly improved its winter survival. Concentrations of sugars and proteins in buds and roots of the dormant selection of CUF 101 increased to values similar to those observed for the fall‐dormant, winter‐hardy Norseman. Selection solely for contrasting fall dormancy can alter cold acclimation in buds and roots and winter survival of alfalfa.

A study was conducted in 2006 and 2007 designed to examine the foraging range of honey bees, Apis mellifera (Hymenoptera: Apidae), in a 15.2 km2 area dominated by a 128.9 ha glyphosate-resistant Roundup Ready® alfalfa seed production field and several non-Roundup Ready alfalfa seed production fields (totaling 120.2 ha). Each year, honey bee self-marking devices were placed on 112 selected honey bee colonies originating from nine different apiary locations. The foraging bees exiting each apiary location were uniquely marked so that the apiary of origin and the distance traveled by the marked (field-collected) bees into each of the alfalfa fields could be pinpointed. Honey bee self-marking devices were installed on 14.4 and 11.2% of the total hives located within the research area in 2006 and 2007, respectively. The frequency of field-collected bees possessing a distinct mark was similar, averaging 14.0% in 2006 and 12.6% in 2007. A grand total of 12,266 bees were collected from the various alfalfa fields on seven sampling dates over the course of the study. The distances traveled by marked bees ranged from a minimum of 45 m to a maximum of 5983 m. On average, marked bees were recovered ∼ 800 m from their apiary of origin and the recovery rate of marked bees decreased exponentially as the distance from the apiary of origin increased. Ultimately, these data will be used to identify the extent of pollen-mediated gene flow from Roundup Ready to conventional alfalfa.

Alfalfa and cotton flowers were pierced with small glass capillaries of an overall size and shape similar to that of Lygus stylets, and injected with small quantities (6 to 100 nL) of solutions that contained Lygus salivary enzymes. Crude and partially purified protein solutions from Lygus heads and isolated salivary glands showed substantial polygalacturonase (PG) activity, as has been previously reported. Following injection with both crude and partially purified protein solutions, as well as with pure fungal and bacterial PGs, flowers of both alfalfa and cotton exhibited damage similar to that caused by Lygus feeding. Injection with the same volume of a buffer control as well as a buffer control containing BSA at a comparable protein concentration (approximately 6 microg/mL) showed no symptoms. These results are consistent with a previously suggested hypothesis that the extensive tissue damage caused by Lygus feeding is primarily due to the action of the PG enzyme on the host tissue, rather than to mechanical damage caused by the insect stylet. Substantial genotypic variation for a PG inhibiting protein (PGIP) exists in alfalfa and cotton. We, therefore, suggest that breeding and selection for increased native PGIP levels, or transformation with genes encoding PGIP from other plant species, may be of value in obtaining alfalfa and cotton varieties that are more resistant to Lygus feeding damage.

Fall dormancy is positively associated with alfalfa (Medicago sativa L.) winter survival, but the physiological bases for this association are not understood. Our objective was to determine how incremental changes in fall dormancy due to genetic selection influenced autumn height and winter survival, root physiology, and expression of a cold acclimation responsive gene family. Seed from each of three cycles of selection for contrasting (greater or less) fall dormancy using ‘Mesilla’ and ‘CUF 101’ as parents were planted in rows in the field (Starks‐Fincastle, fine‐silty, mixed, mesic, Aeric Ochraqualf) in West Lafayette, IN, in May 1997 and 1998. Plant height was measured in October and roots were sampled in December. Plant survival was determined in March of the year following seeding. Fall dormancy (reduction in shoot height in October) increased in a linear manner over the three cycles of selection for both Mesilla and CUF 101. A positive linear relationship was observed between fall height and winter injury in both years. Root sugar and protein concentrations increased as fall dormancy increased in populations derived from both Mesilla and CUF 101. Expression of the cold acclimation‐responsive gene, RootCAR1, was positively associated with winter survival, and may be useful as a molecular marker for identifying winter hardy plants among semi‐dormant or nondormant alfalfa germplasm in December of the seeding year.