William B. Miller

Carbohydrate and amino acid composition of phloem sap and honeydew produced by Bemisia tabaci

Abstract A Florida strain of sweet potato whitefly, Bemisia tabaci (Gennadius), was found to have an expanded range which includes several new food crops. To determine why, we examined how it processes plant nutrients. The amino acid and carbohydrate content of phloem sap from poinsettia and pumpkin and of honeydew produced by the Florida strain were analysed. Honeydews produced by a strain from Arizona feeding on both plants were also analysed. Poinsettia phloem sap contained 15 amino acids; 14 of these were in pumpkin phloem sap. Almost all the same amino acids were in the honeydews produced by the two strains on the two hosts. Approximately half of the amino acids found in the honeydew were at concentrations which were significantly lower than concentrations in the phloem sap. Honeydew from both hosts contained six additional amino acids. The major one was glutanine which may be used to expel nitrogen. Carbohydrates in phloem sap and honeydew were common transport sugars, like sucrose. Both honeydews contained trehalulose, a disaccharide not previously associated with insects. Both strains processed phloem sap and honeydew from both plants in the same manner, but the Florida strain produced significantly larger quantities of honeydew; it is therefore assumed to process more phloem sap. Since this strain has access to more phloem sap it also has access to more of the amino acids which are in short supply in the phloem sap of some plants allowing it to broaden its range.

Effect of low temperature on dormancy breaking and growth after planting in lily bulblets regenerated in vitro

Lilies regenerating on scale segments may develop dormancy in vitro depending on the culture conditions. The dormancy is broken by storage for several weeks at a low temperature (5 °C). The effect of the low temperature on sprouting, time of leaf emergence and further bulb growth was studied. Dormant and non-dormant bulblets were regenerated in vitro on bulb scale segments cultured at 20 °C or 15 °C, respectively. The low temperature not only affected the number of sprouted bulblets but also the time of emergence. The longer the cold storage, the faster and more uniform leaf emergence occurred. Both dormant and non-dormant bulblets grew faster after a low temperature treatment of six weeks. Thus, during dormancy breaking the tissue is prepared not only for sprouting but also for subsequent bulb growth. These processes are rather independent as low temperature stimulates growth in non-dormant bulblets whereas these bulblets sprout also without treatment at low temperature. Moreover, the hormone gibberellin induces rapid sprouting but has no influence on further bulb growth. Good growth in bulblets exposed to the low temperature coincided with production of an increased leaf weight. However, the relationship is not absolute as bulblets that were cold-treated for six weeks grew larger than bulblets cold-treated for four weeks but the formation of leaf biomass was similar. During storage at low temperature starch was hydrolyzed in the bulb scales and sugars accumulated. This indicates that during this period, preparation for later bulb growth involves mobilization of carbohydrate reserves which play a role in leaf growth and development of the photosynthetic apparatus. Starch hydrolysis proceeded in the outer scales after planting. Approximately six weeks later, the switch from source to sink took place in the bulblet, which became visible as a deposition of starch in the middle scales.

Preventive mechanisms of gibberellin4+7 and light on low-temperature-induced leaf senescence in Lilium cv. Stargazer

Abstract Lilium cv. Stargazer plants were held for 2 weeks at 4°C, either in darkness or in light (40 μmol m −2 s −1 ). Another series of plants was held in darkness after pre-treatment with 100 mg l −1 GA 4+7 . Changes in major senescence parameters were determined during storage at 4°C and during 6 days after transferring the plants to 22°C. Foliar sprays of GA 4+7 or supplemental light prevented rapid leaf senescence induced by dark low-temperature storage. During storage at 4°C, basal leaves showed no significant changes in concentrations of chlorophyll, soluble proteins, lipid peroxidation, and activity of catalase. However, shifting from 4 to 22°C induced a series of changes in basal leaves of dark-held plants including rapid loss of chlorophyll, proteolysis, increased lipid peroxidation and loss of catalase activity. Both light and GA 4+7 treatments prevented these changes. Total soluble carbohydrates decreased gradually during 4°C dark storage and after transferring to 22°C. GA 4+7 treatments did not prevent the decline in carbohydrate levels at 4°C, but prevented it upon transferring to 22°C. Supplemental light during 4°C storage significantly increased soluble carbohydrate concentration. The abrupt increases in metabolic activities by shifting from 4 to 22°C accompanied by oxidative stress in leaves already depleted in reserves during 4°C storage seem to induce leaf senescence in dark-held plants.

Stickiness Potential of Individual Insect Honeydew Carbohydrates on Cotton Lint

Stickiness of cotton fiber is usually caused by honeydew deposits from phloem- feeding insects, including whiteflies and aphids. This work was conducted to determine if the specific sugars commonly found in insect honeydews have different stickiness properties when applied to cotton lint. Standard sugar solutions were applied to non sticky cotton lint using a chromatography sprayer and assessed for stickiness using a minicard. The results indicate significant variation in natural stickiness within the sugars commonly found in insect honeydews. Trehalulose, a major component of sweet potato whitefly (Bemisia tabaci) honeydew, was very sticky, as were turanose, palatinose, and sucrose. Melezitose, raffinose, glucose, and fructose were relatively nonsticky. Oligosaccharide stickiness was not directly related to the oligomer chain length, at least up to DP 3. These results suggest efforts to exploit biological methods to ameliorate honeydew-affected lint should focus on sugar components known to be sticky.

Gibberellin-mediated changes in carbohydrate metabolism during flower stalk elongation in tulips

We investigated the effects of a gibberellin synthesis inhibitor (ancymidol) and gibberellin (GA4+7) on carbohydrate metabolism and elongation in internodes of the tulip (Tulipa gesneriana L.) flower stalk during greenhouse growth. During the initial stages of flower stalk growth, the lowermost internode was mainly responsible for total flower stalk length, whereas the uppermost internode mostly contributed to total length during later stages. High concentrations of hexose sugar (mainly glucose) and increased activity of acid invertase were observed when internodes were rapidly elongating. Inhibition of gibberellin biosynthesis with ancymidol reduced the elongation rate of internodes, and inhibited the hexose sugar accumulation and acid invertase activity. Application of GA4+7 to ancymidol-treated plants reversed these effects. The degree of response to ancymidol and GA4+7 was, however, different in different internodes such that the lowermost internode was most responsive and the uppermost internode was least responsive. The results indicate that de novo biosynthesis of gibberellins is a requirement for expression of high acid invertase activity during the rapid elongation phase in tulip internodes which enables cleavage of imported sucrose to hexoses that can be readily utilized in elongating cells.

Changes in soluble carbohydrates during phytochrome-regulated petiole elongation in watermelon seedlings

Changes in soluble carbohydrate composition and concentration in leavesand petioles of watermelon (Citrullus lanatus (Thunb)Matsum and Nakai cv. Sugar Baby) seedlings during early stages ofphytochrome-regulated petiole elongation were investigated. Watermelon seedlingswere grown in a controlled environment with 350 μmolm−2 s−1 photosynthetically activeradiation (PAR) during a 12-h photoperiod. Low intensity end-of-day(EOD) light treatments (for 15 min) of red (R), far-red (FR) and FRfollowed by R (FR/R) were initiated when the seedlings were 14 days old.Seedling growth, and soluble carbohydrate concentration and composition inleaves and petioles were determined after 3 and 6 days of EOD light treatments.The EOD FR increased the petiole length and dry mass partitioned to petioles asearly as 3 days into the treatment. This increased petiole dry mass inFR-treated plants was accompanied with an increase in reducing sugar (glucoseand fructose) concentration in the petioles. Although both leaves and petiolesshowed this effect, the relative increase was greater in petioles than leaves.While the most abundant sugars in petioles were fructose and glucose, thepredominant sugars in leaves were sucrose, raffinose, and stachyose. Thephotoreversion of FR induced changes in growth and sugar concentrations by Rindicates the involvement of phytochrome in these processes.

Microcrystallography, high-pressure cryocooling and BioSAXS at MacCHESS

Three research initiatives pursued by the Macromolecular Diffraction Facility at the Cornell High Energy Synchrotron Source (MacCHESS) are presented.

Variations in zonal fruit starch concentrations of apples – a developmental phenomenon or an indication of ripening?

Patterns of starch hydrolysis in stem, equatorial, and calyx zones of ‘Honeycrisp’ and ‘Empire’ apples (Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) during maturation and ripening, and in ‘Gala’ apples in response to propylene or 1-methylcyclopropene (1-MCP) treatments after harvest, were studied. Differences in zonal starch concentrations were found for ‘Empire’ and ‘Gala’ fruits, but not for ‘Honeycrisp’. During maturation and ripening of ‘Empire’, the concentration of starch was highest in the calyx end and lowest in the stem region.</title> Differences in rates of starch hydrolysis among zones were not detected. ‘Honeycrisp’ and ‘Empire’ had the highest concentration of sorbitol in the calyx region, whereas it was highest in the stem-end region in ‘Gala’. The distribution differences of glucose, fructose, and sucrose were similar in all three cultivars; higher fructose and glucose concentrations in the stem region, and higher sucrose concentrations in the calyx end of the fruit. Postharvest treatment of ‘Gala’ with propylene did not affect the internal ethylene concentration of the fruit but 1-MCP markedly inhibited it. Starch concentrations were highest in the calyx end but gradients of starch among zones were not changed by postharvest treatment. The rate of hydrolysis was slowed by 1-MCP treatment, but was unaffected by propylene. Postharvest treatments influenced sorbitol, glucose, and fructose concentrations. Patterns of starch concentration among the zones did not confirm differences in ripening, but reflected its uneven distribution throughout the fruit during development. Therefore, measured differences in zonal starch are most likely related to starch accumulation during fruit development, rather than differences in rates of starch degradation during ripening.

Carbohydrate status and postharvest leaf chlorosis of miniature roses as influenced by carbon dioxide enrichment

Abstract The effect of CO2 enrichment on carbohydrate status and postharvest leaf chlorosis of potted ‘Meijikatar’ miniature roses was investigated. Plants were grown in 350, 700 or 1050 μl l−1 CO2 until they reached flower bud coloration and placed into dark storage at 4°C or 16°C for 5 days to simulate shipping before placing in an interior environment with a photon flux of 30 μmol m−2 s−1 from cool white fluorescent light source for postharvest evaluation. Stomatal resistance was increased (∼25%) and aperture was decreased (∼36%) by 700 or 1050 compared to 350 μ1 1−1 CO2. The higher CO2 levels slightly (10%) increased leaf sucrose concentration, had no effect on stem sucrose concentration, and had little effect on whole plant reducing sugars. Leaf and stem starch concentration increased over three-fold as CO2 increased from 350 to 700 μ1 1−1. Regardless of storage temperature, carbon dioxide enrichment did not affect the overall visual quality or percentage leaf chlorosis after 5 days in the interior environment. Regardless of CO2 level, plants stored at 16°C showed three-fold increase in leaf chlorosis compared to plants stored at 4°C. Although CO2 enrichment increased the carbohydrate pools of the plants, our results do not support the hypothesis that increased carbohydrate supply plays a role in reduction of postharvest leaf chlorosis of potted miniature roses.

Nitrate: ammonium ratio affects growth and development of Oxalis regnellii in hydroponic culture.

Nitrogen (N)-source ratio (NO3 -:NH4 +) effects on growth and development of oxalis have not been investigated previously. An experiment was conducted to establish an optimum NO3 -:NH4 + ratio for oxalis in a hydroponic system. Five NO3 --N:NH4 +-N ratio treatments consisting of 100:0, 75:25, 50:50, 25:75, and 0:100 were tested. Increasing proportions of NO3 --N increased total leaf, root, flower, and bottom shoot biomasses. New rhizome biomass increased with increasing NO3 --N rates until 50 and 75%, after which, new rhizome biomass decreased. Plants that received increasing amounts of NO3 --N were greener or had a greater chlorophyll index at the end of the experiment. On a dry weight basis, N, B, Fe, and Al concentrations decreased as NO3 --N levels increased, whereas K, Ca, and Mn concentrations increased. Tissue P, Mo, and Cu increased with increasing NO3 --N levels up to 50% NO3 --N supplied, and then decreased. No significant relationship was found with NO3 -: NH4 + ratios for Mg, Zn, and Na.