Carotenoid Biosynthesis during Tomato Fruit Development (Evidence for Tissue-Specific Gene Expression)

Area of Science:

• Plant Biochemistry
• Molecular Biology
• Fruit Development

Background:

• Carotenoids and chlorophylls are key pigments in tomato fruit development.
• Enzyme activities and gene expression of carotenoid biosynthesis pathway enzymes are crucial for pigment accumulation.

Purpose of the Study:

• To analyze carotenoid and chlorophyll content, enzyme activities, and gene expression during tomato fruit development.
• To investigate the regulation of carotenogenic genes (Psy and Pds) and identify potential isoforms of key enzymes.

Main Methods:

• Analysis of pigment content, in vitro enzyme activities (phytoene synthase, phytoene desaturase, lycopene cyclase), and gene expression (Psy, Pds) at five developmental stages.
• Northern blot analysis for gene expression and Western blot analysis using specific antibodies to differentiate enzyme isoforms.
• Determination of molecular masses of phytoene synthase from green and ripe fruit.

Main Results:

• Total carotenoids increased during ripening, while chlorophyll decreased.
• Highest carotenogenic enzyme activities were observed in green fruit, despite lower carotenoid content.
• Psy and Pds gene expression was elevated in chromoplast-containing tissues (breaker and ripe fruit) and flowers, but not detectable in green fruit or leaves by Northern blot.
• Western blot analysis and molecular mass differences (42 kD in green fruit, 38 kD in ripe fruit) suggest divergent phytoene synthase enzymes.

Conclusions:

• Carotenoid biosynthesis is regulated developmentally, with Psy and Pds gene transcription significantly increasing in chromoplast-containing tissues.
• The presence of distinct phytoene synthase enzymes in green and ripe tomatoes supports the hypothesis of divergent genes encoding these enzymes.
• Enzyme activity and gene expression patterns indicate complex regulation of carotenoid accumulation during tomato fruit ripening.