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The principles of plant physiology are best learned in an environment where students are directly engaged in the process of scientific inquiry. Working from this assumption, we have developed a two-stage approach to laboratory instruction that fosters student-directed research within an undergraduate plant physiology course. During the first 10 weeks of a 16-week semester, students develop competency in measuring physiological variables by using an array of standard analytical techniques. A core set of 10 laboratory experiments provides structured instruction and teaches the principles of modern physiological analyses. During week 11, students observe a demonstration of a plant response, where the underlying cause of the phenomenon is not evident. Working together in groups of three or four, students hypothesize on the physiological mechanisms that may be involved. After submitting a statement of hypothesis and a plan of study, each group then requests the necessary instrumentation, plant material and greenhouse and/or growth chamber space to conduct their experiments. Results of their experimentation are presented during week 15 in both written and oral formats. The approach appears to help students to integrate and connect learnings from earlier in the semester to solve a defined problem. Further, students learn how to judge the reliability of experimental results and to evaluate whether conclusions drawn are justified by the data.
Abstract
Ethylene production by wounded sweet potato (Ipomoea batatas L.) roots varied with storage time and method of wounding. Preliminary experiments showed that wounded cured roots produced more ethylene than freshly harvested roots and roots held in 15°C storage for up to 22 weeks. The longer the sweet potato roots were in storage, the greater the ethylene production from wounded roots. On average, broken roots produced 30% more ethylene than cut roots. Maximum ethylene production occurred 2 to 4 days after wounding. Since ethylene was not detectable 6 hr after injury, it should be referred to as stress-induced rather than wound ethylene.
Abstract
‘Forever Yours’ roses (Rosa Hybrid Tea) were grown in recirculating nutrient solutions at 0.25, 2.5, 5.0 and 10.0 meq K/liter. Low K supply (0.25 and 2.5 meq/liter) reduced growth, flower production, and length of flowering stems. Leaf K concentration was reduced at the lowest K concentration in solution. Increasing K concentration in solution from 0.25 to 10.0 meq/liter had no antagonistic effect on the accumulation of Ca or Mg in the leaves. Plants which received 0.25 meq K/liter developed K deficiency symptoms after 5 weeks of growth in treatment solutions.
Abstract
Changes in dry weights, total N, nitrate N, and reduced N in the aboveground parts of Chrysanthemum × morifolium Ramat. ‘Gt.#4 Indianapolis White’ were determined at intervals from planting of rooted cuttings until inflorescence maturity. Plant dry matter accumulation rate (mg/day) increased in the combined aboveground tissues with each successive harvest, while N accumulation rate (mg N/day) peaked early in the plants’ growth and decreased after the 6th week of growth. Continued dry matter accumulation in the leaves during inflorescence development suggested that photosynthetic capacity was in excess of the inflorescences’ needs. In contrast, a loss of N from the vegetative portions, and primarily the stems plus petioles, indicated that newly absorbed N was inadequate to meet the demands of the developing inflorescence. The partitioning of N between NO3 and reduced N indicated that enzymatic reduction of NO3 did not limit the availability of reduced N during inflorescence development.
Abstract
‘Forever Yours’ roses (Rosa Hybrid Tea) were grown in recirculating nutrient solutions at 1.0 and 10.0 meq/liter K in combination with 10.0 meq/liter NO3-N or NH4-N. Low K limited the growth and flower production, regardless of N form. Ammonium-N fertilized plants showed NH4-N toxicity symptoms as interveinal chlorosis of the lower leaflets. An increased K supply reduced NH4-N toxicity symptoms. Concentrations of Ca and Mg were lower, while P was higher, in the tissue of NH4-N fertilized plants, as compared to NO3-N fertilized plants. Total N, alcohol insoluble N, soluble organic N, and NH4-N were higher in the tissue of plants which received NH4-N, as compared to NO3-N, regardless of K level. An increased K supply from 1.0 to 10.0 meq/liter resulted in higher NO3-N in NO3-N fertilized plants and lower NH4-N in NH4-N fertilized plants.
Abstract
Rooted cuttings of Chrysanthemum × morifolium Ramat. ‘Gt. #4 Indianapolis White’ were grown in a greenhouse in a sand culture and supplied with either 3.75 or 15.0 mm