Proline is a proteogenic amino acid and accumulates both under stress and non-stress conditions as a beneficial solute in plants. Recent discoveries point out that proline plays an important role in plant growth and differentiation across life cycle. It is a key determinant of many cell wall proteins that plays important roles in plant development. The role of extensins, arabinogalactan proteins and hydroxyproline- and proline-rich proteins as important components of cell wall proteins that play pivotal roles in cell wall signal transduction cascades, plant development and stress tolerance is discussed in this review. Molecular insights are also provided here into the plausible roles of proline transporters modulating key events in plant development. In addition, the roles of proline during seed developmental transitions including storage protein synthesis are discussed.

Aluminum (Al) stress is one of the serious limiting factors in plant productivity in acidic soils, which constitute about 50 % of the world's potentially arable lands and causes anywhere between 25 and 80 % of yield losses depending upon the species. The mechanism of Al toxicity and tolerance has been examined in plants, which is vital for crop improvement and enhanced food production in the future. Two mechanisms that facilitate Al tolerance in plants are Al exclusion from the roots and the ability to tolerate Al in the symplast or both. Although efforts have been made to unravel Al-resistant factors, many aspects remain unclear. Certain gene families such as MATE, ALMT, ASR, and ABC transporters have been implicated in some plants for resistance to Al which would enhance the opportunities for creating crop plants suitable to grow in acidic soils. Though QTLs have been identified related to Al-tolerance, no crop plant that is tolerant to Al has been evolved so far using breeding or molecular approaches. The remarkable changes that plants experience at the physiological, biochemical and molecular level under Al stress, the vast array of genes involved in Al toxicity-tolerance, the underlying signaling events and the holistic image of the molecular regulation, and the possibility of creating transgenics for Al tolerance are discussed in this review.

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cDNA and genomic clones of cinnamoyl CoA reductase measuring 1011 and 2992 bp were isolated from a leguminous pulpwood tree Leucaena leucocephala, named as LlCCR. The cDNA exhibited 80-85% homology both at the nucleotide and amino acid levels with other known sequences. The genomic sequence contained five exons and four introns. Sense and antisense constructs of LlCCR were introduced in tobacco plants to up and down-regulate this key enzyme of lignification. The primary transformants showed a good correlation between CCR transcript levels and its activity. Most of the CCR down-regulated lines displayed stunted growth and development, wrinkled leaves and delayed senescence. These lines accumulated unusual phenolics like ferulic and sinapic acids in cell wall. Histochemical staining suggested reduction in aldehyde units and increased syringyl over guaiacyl (S/G) ratio of lignin. Anatomical studies showed thin walled, elongated xylem fibres, collapsed vessels with drastic reduction of secondary xylem. The transmission electron microscopic studies revealed modification of ultrastructure and topochemical distribution of wall polysaccharides and lignin in the xylem fibres. CCR down-regulated lines showed increased thickness of secondary wall layers and poor lignification of S2 and S3 wall layers. The severely down-regulated line AS17 exhibited 24.7% reduction of Klason lignin with an increase of 15% holocellulose content. Contrarily, the CCR up-regulated lines exhibited robust growth, development and significant increase in lignin content. The altered lignin profiles observed in transgenic tobacco lines support a role for CCR down-regulation in improving wood properties of L. leucocephala exclusively used in the pulp and paper industry of India.