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Title: SENSITIVE AND RESISTANT LINES OF SNAPBEAN (PHASEOLUS VULGARIS L.) II. DAILY WATER USE.

Author
item Fiscus, Edwin
item Flowers, Michael
item Booker, Fitzgerald
item Burkey, Kent

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/2005
Publication Date: 8/5/2005
Citation: Fiscus, E.L., Flowers, M.D., Booker, F.L., Burkey, K.O. Sensitive and resistant lines of snapbean (Phaseolus vulgaris L.) II. daily water use.American Society of Plant Biologists Annual Meeting.

Interpretive Summary: The daily water use of ozone sensitive and resistant lines of snapbean was studied in an attempt to shed some light on the reasons for the differences in sensitivity to this air pollutant. Daily water use was measured by continuously weighing the pots on electronic scales in a controlled environment system. The resistant line suffered damage from ozone exposure and as a result of the damage restricted its daily water loss which is a normal response to sustaining damage to the photosynthetic apparatus. Water loss, as well as ozone entry, occurs through the leaf stomata and in a normal plant when water loss is restricted by partial closure of stomata, ozone entry is also restricted, thus limiting the degree of damage. However, in the sensitive lines the normal ability to restrict stomatal opening and water loss seems to be lacking. This condition permits much more extensive entry of damaging ozone to the leaf interior where massive damage accumulates leading to large reductions in plant growth and productivity.

Technical Abstract: Experiments were conducted to determine the relative growth, yield and selected physiological responses of ozone resistant (R331) and sensitive (S156) lines of snapbean Phaseolus vulgaris to a range of chronic Ozone exposures. Plants were grown in mini-greenhouses in the field which allow 90% of full daily irradiation and control of temperature, humidity and gas composition. As part of these experiments we examined the whole plant water use characteristics to determine if the sensitivity to ozone might be related to inadequate stomatal control in the S156 line. The exposure-response experiment was replicated 4 times during 2003 and 2004. At 12h mean [O3] = 60 nLL-1 seed yield in S156 was reduced by 77% while only a 34% reduction was noted for R331. Seasonal water use was reduced by half in R331, most of which was probably due to reduced plant size. However, water use by S156 was reduced by only 14% in spite of its much reduced size. Water use efficiency (WUE) increased 35% in R331 due to a larger proportional decrease in water use than yield, while in S156 WUE was dramatically reduced (by 73%) both because of a larger yield reduction and a much smaller reduction in water use in the 60 nLL-1 treatment. Taken together these data suggest that even though S156 was sustaining greater levels of damage to its photosynthetic systems, growth and reproductive capacity the feedback control regulating stomatal conductance (gs), thus daily whole plant water loss, was compromised. The apparent inconsistencies between daily water loss and midday gs may result from the practice of sampling only upper canopy leaves for gs while water loss is occurring throughout the canopy. Additional, more thorough studies are required to clarify these relationships.