Theses and Dissertations

Issuing Body

Mississippi State University


Harkess, Richard L.

Committee Member

Bi, Guihong

Committee Member

Denny, Geoff C.

Committee Member

Henry, W. Brien

Date of Degree


Document Type

Graduate Thesis - Open Access


Plant and Soil Sciences (Horticulture)

Degree Name

Master of Science


College of Agriculture and Life Sciences


Department of Plant and Soil Sciences


Developing foliar growth of ivy geraniums (Pelargonium peltatum) bleaches white after exposure to temperatures greater than 30°C. This study investigated chloroplast development in ivy geraniums under heat stress comparing a heat sensitive cultivar, Temprano™ Lavender, and a heat tolerant cultivar, Contessa™ Red. Using transmission electron microscopy and spectrophotometry, foliar bleaching under heat stress was found to be due to an absence of developed chloroplasts within the bleached new growth accompanied by lower chlorophyll content. To determine whether heat stress related foliar bleaching could be prevented, cytokinin and gibberellins were applied in combination, at different rates before, during or after a heat stress event. Applying 50 to 100 ppm gibberellins before heat stress reduced bleaching in new growth. Gibberellins applied at 50 ppm within a week of a heat stress event decreased bleaching. Net photosynthesis and chlorophyll fluorescence was greater in non-heat stressed plants than heat stressed plants.