Differential effects of NAA and 2,4-D in reducing floret abscission in cestrum (Cestrum elegans) cut flowers are associated with their differential activation of Aux/IAA homologous genes.
OBJECTIVE
A previous study showed that the relative effectiveness of 2,4-dichlorophenoxyacetic acid (2,4-D) compared with that of 1-naphthaleneacetic acid (NAA) in reducing floret bud abscission in cestrum (Cestrum elegans) cut flowers was due to its acropetal transport. The aim of the present study was to examine if the differential effect of these auxins on floret abscission is reflected in the expression of Aux/IAA genes in the floret abscission zone (AZ).


METHODS
cDNAs were isolated by PCR-based cloning from the floret AZ of auxin-treated cut flowers. The expression patterns of the cDNAs in various tissues and the effect of indole-3-acetic acid (IAA), applied with or without cycloheximide, on their expression in the floret AZ were examined by northern blot analysis. The regulation of transcript accumulation in the floret AZ in response to NAA or 2,4-D was measured by real-time PCR during auxin pulsing of cut flowers and vase life, concomitantly with floret abscission.


RESULTS
Six isolated cDNAs were identified to represent Aux/IAA homologous genes, designated as Cestrum elegans (Ce)-IAA1 to Ce-IAA6. Four Ce-IAA genes were characterized as early auxin-responsive genes (ARGs), and two (Ce-IAA1 and Ce-IAA5) as late ARGs. Only Ce-IAA5 was AZ-specific in floret buds. A temporal regulation of Ce-IAA transcript levels in the floret AZ was found, with 2,4-D inducing higher expression levels than NAA in floret buds. These Ce-IAA expression levels were negatively correlated with floret abscission.


CONCLUSIONS
The differential transport characteristics of NAA and 2,4-D in cestrum cut flowers were reflected in differential activation of the Ce-IAA genes identified in the floret AZ. Therefore, Aux/IAA genes can be used as molecular markers to measure auxin activity, which reflects free auxin level in the AZ. Two of the identified genes, Ce-IAA1 and Ce-IAA5, may also have a regulatory role in abscission.
Abebie
Bekele
B
The Kennedy-Leigh Centre for Horticultural Research, The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel.
Lers
Amnon
A
Philosoph-Hadas
Sonia
S
Goren
Raphael
R
Riov
Joseph
J
Meir
Shimon
S
D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D032301:Cestrum / Q000187:drug effects / Q000235:genetics*; D003001:Cloning, Molecular; D003513:Cycloheximide / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D035264:Flowers / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D017343:Genes, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D009280:Naphthaleneacetic Acids / Q000494:pharmacology*; D009928:Organ Specificity / Q000187:drug effects; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid
D018076:DNA, Complementary; D007210:Indoleacetic Acids; D009280:Naphthaleneacetic Acids; D010940:Plant Proteins; D015084:2,4-Dichlorophenoxyacetic Acid; D003513:Cycloheximide