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Gibberellins (GAs) are a group of diterpenoid acids with ent-gibberellane skeleton that function as plant growth regulators influencing a range of devel- opmental processes in higher plants including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, leaf and fruit senes- cence (Graebe and Ropers, 1978). Gibberellic acid is a high value, industrially important biochemical, sell- ing high rate in the international market depending on the purity and potency. Gibberellic acid also has potential application in improving seedling establish- ment and seed production in hybrid rice (Carlson et al., 1992). In India up to 1970’s research on gibberel- lic acid mainly focused on the isolation and identifi- cation of GAs from plant sources. Studies conducted at CFTRI, Mysore in 1970s ended with a GA3 yield of0.40 - 0.45 g per litre in submerged fermentation pro- cess (SmF) even after optimizing the culture condition parameters. The efficient strain selection and usage plays key role to make the gibberellic acid production economically viable. The strain improvement strategy for increased GA production can be achieved by mu- tation and protoplast fusion in filamentous fungi like F.fujikuroi. In the present work, we have screened and developed a procedure to obtain effective F.fujikuroi mutants through physical and chemical mutagenesis for increased gibberellic acid production.

Nonsymbiotic hemoglobins (nsHbs) and leghemoglobins (Lbs) are plant proteins that can reversibly bind O(2) and other ligands. The nsHbs are hexacoordinate and appear to modulate cellular concentrations of NO and maintain energy levels under hypoxic conditions. The Lbs are pentacoordinate and facilitate the diffusion of O(2) to symbiotic bacteroids within legume root nodules. Multiple lines of evidence suggest that all plant Hbs evolved from a common ancestor and that Lbs originated from nsHbs. However, little is known about the structural intermediates that occurred during the evolution of pentacoordinate Lbs from hexacoordinate nsHbs. We have cloned and characterized a Hb (ppHb) from the root nodules of the ancient caesalpinoid legume Chamaecrista fasciculata. Protein sequence, modeling data, and spectral analysis indicated that the properties of ppHb are intermediate between that of nsHb and Lb, suggesting that ppHb resembles a putative ancestral Lb. Predicted structural changes that appear to have occurred during the nsHb to Lb transition were a compaction of the CD-loop and decreased mobility of the distal His inhibiting its ability to coordinate directly with the heme-Fe, leading to a pentacoordinate protein. Other predicted changes include shortening of the N- and C-termini, compaction of the protein into a globular structure, disappearance of positive charges outside the heme pocket and appearance of negative charges in an area located between the N- and C-termini. A major consequence for some of these changes appears to be the decrease in O(2)-affinity of ancestral nsHb, which resulted in the origin of the symbiotic function of Lbs.

Amino acid sequences for more than 60 plant hemoglobins (Hbs) are deposited in databases, but the tertiary structure of only 4 plant Hbs have been reported; thus, the gap between the reported sequences and structures of plant Hbs is large. Elucidating the structure of plant Hbs is essential to fully understanding the function of these proteins in plant cells. Determining the actual protein structure by experimental methods (i.e., by X‐ray crystallography) requires considerable protein material and is expensive; thus, this type of work is limited to few laboratories around the world. In silico (computer) methods to predict the tertiary structure of proteins from amino acid sequences have been implemented and are helping reduce the sequence‐structure gap. Thus, in silico methods are useful tools for predicting the tertiary structure of several plant Hbs from amino acid sequences deposited in databases. In this chapter, we describe a method for predicting and analyzing the structure of a rice Hb2 from the template structure of native rice Hb1. This method is based on a comparative modeling method that uses programs from the SWISS‐MODEL server.

This review describes contributions to the study of plant hemoglobins (Hbs) from a historical perspective with emphasis on non-symbiotic Hbs (nsHbs). Plant Hbs were first identified in soybean root nodules, are known as leghemoglobins (Lbs) and have been characterized in detail. It is widely accepted that a function of Lbs in nodules is to facilitate the diffusion of O(2) to bacteroids. For many years Hbs could not be identified in plants other than N(2)-fixing legumes, however in the 1980s a Hb was isolated from the nodules of the non-legume dicot plant Parasponia, a hb gene was cloned from the non-nodulating Trema, and Hbs were detected in nodules of actinorhizal plants. Gene expression analysis showed that Trema Hb transcripts exist in non-symbiotic roots. In the 1990s nsHb sequences were also identified in monocot and primitive (bryophyte) plants. In addition to Lbs and nsHbs, Hb sequences that are similar to microbial truncated (2/2) Hbs were also detected in plants. Plant nsHbs have been characterized in detail. These proteins have very high O(2)-affinities because of an extremely low O(2)-dissociation constant. Analysis of rice Hb1 showed that distal His coordinates heme Fe and stabilizes bound O(2); this means that O(2) is not released easily from oxygenated nsHbs. Non-symbiotic hb genes are expressed in specific plant tissues, and overexpress in organs of stressed plants. These observations suggest that nsHbs have functions additional to O(2)-transport, such as to modulate levels of ATP and NO.