Botany & Zoology
Welcome to Stellenbosch University

Prof. Alex Valentine

Research focus

Our group is interested in the molecular plant physiology of phosphorus nutrition during plant-microbe interactions. We are currently focussing on the phosphorus nutrition of legumes in symbiosis with yeasts, mycorrhizas and nitrogen fixing bacteria. The research approach is to study the function and regulation of plant-microbe interactions, using physiological and molecular biological tools. In this regard, we are integrating classical plant physiological methods with modern tools such as qRT-PCR, micro-array analysis, proteomics and retro-transposon insertional-mutant lines of Medicago truncatula. Various legumes are being used in specific projects, which include model legumes, indigenous legume, invasive legumes and crop legumes.

Current projects


1) Carbon and nitrogen metabolism in phosphorus deficient nodules of legumes.

a) The regulation of PEPc isoforms in the phosphorus deficient nodules (PHD project)

b) The role malate metabolism in phosphorus deficient nodules (current PHD project)

c) The carbon costs of N nutrition via biological nitrogen fixation and mycorrhizal symbiosis in phosphorus deficient legumes (current PhD project)

d) Roles of micro-RNA and transcription factors during recovery from phosphorus deficiency in legume nodules (available project)

e) Respiratory and photosynthetic carbon costs of nitrogen fixation during P deficiency (available project)

2) Diurnal and circadian regulation of nitrogen fixation in the model legume, Medicago truncatula.

a) Diurnal and circadian regulation of nitrogen fixation by metabolic gene expression networks and respiratory carbon costs (In collaboration with Udvardi laboratory at the Noble Foundation, USA)

b) Nodule clock genes controlling circadian rhythms and expression networks in Medicago truncatula (In collaboration with Udvardi laboratory at the Noble Foundation, USA)

3) Phosphorus nutrition of a retro-transposon insertional-mutant of Medicago truncatula, that forms arbuscule-free mycorrhizal roots.

a) Function of high and low affinity P-transporters in roots and nodules during phosphate starvation (available project)

b) Carbon costs of P acquisition in arbuscule-free roots and nodules during phosphate starvation (available project)

Current team members

Aleysia Kleinert (PhD completed 2010); Karen Cloete (PhD completed 2010); Marcellous Le Roux (PhD student); Peter Mortimer (PhD student); Mark Maistry (PhD student); Chris Daniels (PhD student).

We currently have openings for funded projects at Honours, MSc and PhD levels.

Former lab members
PhD: Aleysia Kleinert, Karen Cloete

MSc: Melissa Lintnaar, Simeon Hengari, Peter Mortimer, Marcellous Le Roux, Caroline Ward, Albertina Ndeinoma, Karen Cloete, Andre Meyer


Daniels, C. W., Rautenbach, F., Marnewick, J. L., Valentine, A. J., Babajide, O. J., & Mabusela, W. T. (2015). Environmental stress effect on the phytochemistry and antioxidant activity of a south african bulbous geophyte, gethyllis multifolia L. bolus. South African Journal of Botany, 96, 29-36.

Maistry, P. M., Muasya, A. M., Valentine, A. J., & Chimphango, S. B. M. (2015). Balanced allocation of organic acids and biomass for phosphorus and nitrogen demand in the fynbos legume podalyria calyptrata. Journal of Plant Physiology, 174, 16-25.

Maistry, P. M., Muasya, A. M., Valentine, A. J., & Chimphango, S. B. M. (2015). Increasing nitrogen supply stimulates phosphorus acquisition mechanisms in the fynbos species aspalathus linearis.Functional Plant Biology, 42(1), 52-62.

Kleinert, A., Venter, M., Kossmann, J., & Valentine, A. (2014). The reallocation of carbon in P deficient lupins affects biological nitrogen fixation. Journal of Plant Physiology, 171(17), 1619-1624.

Le Roux, M., Phiri, E., Khan, W., Şakiroglu, M., Valentine, A., & Khan, S. (2014). Expression of novel cytosolic malate dehydrogenases (cMDH) in lupinus angustifolius nodules during phosphorus starvation. Journal of Plant Physiology, 171(17), 1609-1618.

Lötter, D., Archer Van Garderen, E., Tadross, M., & Valentine, A. J. (2014). Seasonal variation in the nitrogen nutrition and carbon assimilation in wild and cultivated aspalathus linearis (rooibos tea).Australian Journal of Botany, 62(1), 65-73.

Lotter, D., Valentine, A. J., Archer Van Garderen, E., & Tadross, M. (2014). Physiological responses of a fynbos legume, aspalathus linearis to drought stress. South African Journal of Botany, 94, 218-223.

Magadlela, A., Kleinert, A., Dreyer, L. L., & Valentine, A. J. (2014). Low-phosphorus conditions affect the nitrogen nutrition and associated carbon costs of two legume tree species from a mediterranean-type ecosystem. Australian Journal of Botany, 62(1), 1-9.

Thuynsma, R., Valentine, A., & Kleinert, A. (2014). Phosphorus deficiency affects the allocation of below-ground resources to combined cluster roots and nodules in lupinus albus. Journal of Plant Physiology, 171(3-4), 285-291.

Thuynsma, R., Valentine, A., & Kleinert, A. (2014). Short-term supply of elevated phosphate alters the belowground carbon allocation costs and functions of lupin cluster roots and nodules. Journal of Plant Physiology, 171(8), 648-654.

Vardien, W., Mesjasz-Przybylowicz, J., Przybylowicz, W. J., Wang, Y., Steenkamp, E. T., & Valentine, A. J. (2014). Nodules from fynbos legume virgilia divaricata have high functional plasticity under variable P supply levels. Journal of Plant Physiology, 171(18), 1732-1739.

Daniels, C., Mabusela, W., Marnewick, J., & Valentine, A. (2013). The carbon and nitrogen cost associated with the growth, reproductive and dormant phases of two south african semi-arid geophytic species of gethyllis (amaryllidaceae). Australian Journal of Botany, 61(7), 528-537.

Daniels, C. W., Mabusela, W. T., Marnewick, J. L., & Valentine, A. J. (2013). Photosynthetic adaptation of two semi-arid species of gethyllis (kukumakranka) to drought-and-shade stress. South African Journal of Botany, 88, 36-41.

Mortimer, P. E., Le Roux, M. R., Pérez-Fernández, M. A., Benedito, V. A., Kleinert, A., Xu, J., & Valentine, A. J. (2013). The dual symbiosis between arbuscular mycorrhiza and nitrogen fixing bacteria benefits the growth and nutrition of the woody invasive legume acacia cyclops under nutrient limiting conditions. Plant and Soil, 366(1-2), 229-241.

Valentine, A., Ruzvidzo, O., Kleinert, A., Kang, Y., & Bennedito, V. (2013). Infrared gas analysis technique for the study of the regulation of photosynthetic responses. Methods in Molecular Biology, 1016, pp. 261-269.

Mortimer, P. E., Pérez-Fernández, M. A., & Valentine, A. J. (2012). Arbuscular mycorrhiza maintains nodule function during external NH 4 +supply in phaseolus vulgaris (L.). Mycorrhiza, 22(3), 237-245.

Valentine, A. J., Kleinert, A., & Verdier, J. (2012). The 'atom-splitting' moment of synthetic biology. nuclear physics and synthetic biology share common features. EMBO Reports, 13(8), 677-679.

Ruzvidzo, O., Donaldson, L., Valentine, A., & Gehring, C. (2011). The arabidopsis thaliana natriuretic peptide AtPNP-A is a systemic regulator of leaf dark respiration and signals via the phloem. Journal of Plant Physiology, 168(14), 1710-1714.

Cloete KJ, Valentine AJ, Botha A. (2010) The soil yeast Cryptococcus laurentii alters the photosynthetic and respiratory carbon, nutrient and water economy of a Mediterranean sclerophyll, Agathosma betulina (Berg.) Pillans. Symbiosis (DOI 10.1007/s13199-010-0084-0)

Caroline L. Ward, Aleycia Kleinert, Katia C. Scortecci, Vagner A. Benedito, Alexander J. Valentine (2010). Phosphorus-deficiency reduces aluminium toxicity by altering uptake and metabolism of root zone carbon dioxide. Journal of Plant Physiology (DOI:10.1016/j.jplph.2010.08.005)

Cloete KJ, Przybylowicz WJ, Mesjasz-Przybylowicz J, Barnabas AD, Valentine AJ, Botha A. (2010) Micro-PIXE mapping of elemental distribution in roots of a Mediterranean-type sclerophyll, Agathosma betulina (Berg.) Pillans, colonized by Cryptococcus laurentii. Plant Cell and Environment 33:1005-1015

Valentine AJ (2010) Comment on: “Big Science, little science”. EMBO Reports 11 (3): 152

Valentine AJ, Benedito VA, Kang Y (2010) Abiotic stress in legume N2 fixation: from physiology to genomics and beyond. In: Annual Plant Reviews Volume 42: Nitrogen Metabolism in Plants in the Post-genomic Era. C Foyer M Zhao (eds) Wiley-Blackwell (Oxford) pp 207-248.

Cloete KJ, Valentine AJ, Stander MA, Blomerus LM, Botha A (2009). Evidence of Symbiosis between the Soil Yeast Cryptococcus laurentii and a Sclerophyllous Medicinal Shrub, Agathosma betulina (Berg.) Pillans. Microbial Ecology57 (4):624-632

Gottig N, Garavaglia BS, Daurelio LD, Valentine AJ, Gehring C, Orellano EG, Ottado J (2009) Modulating host homeostasis as a strategy in the plant-pathogen arms race. Communicative and Integrative Biology 2(2): 1-2

Allison l. Gregory, Brenden A. Hurley, Hue T. Tran, Vicki l. Knowles, Alex J. Valentine, Yi-Min She§ and William C. Plaxton (2009) In vivo regulatory phosphorylation of the phosphoenolpyruvate carboxylase AtPPC1 in phosphate-starved Arabidopsis thaliana. The Biochemical Journal 420 (1):57-65

Mortimer PE, Perez-Fernandez MA, Valentine AJ (2009) NH4+ nutrition affects the photosynthetic and respiratory C sinks in the dual symbiosis of a mycorrhizal legume. Soil Biology and Biochemistry 41: 2115–2121.

Mortimer PE, Perez-Fernandez MA, Valentine AJ (2008) Photosynthetic and respiratory C costs of N and P nutrition in the dual symbiosis of a mycorrhizal legume. Soil Biology and Biochemistry 40: 1091-1027

Le Roux MR, Kahn S, Valentine AJ (2008) Organic acid accumulation inhibits N2–fixation in P-stressed lupin nodules. New Phytologist 177 (4): 956-964

Gottig N, Garavaglia BS, Daurelio LD, Valentine AJ, Gehring C, Orellano EG, Ottado J (2008) The bacterial pathogen Xanthomonas axonopodis pv. citri uses a plant natriuretic peptide-like protein to modify host responses - a case of molecular mimicry. Proceedings of the National Academy of Sciences of USA 105(47):18631-18636

Le Roux MR, Kahn S, Valentine AJ (2008) Nodular adaptations to P deficiency in amino acid and ureide exporting legumes, lupins and soybeans. Symbioses 48:102-109

Biological Nitrogen Fixation: Towards Poverty Alleviation Through Sustainable Agriculture. Series: Current Plant Science and Biotechnology in Agriculture (2008). Felix D. Dakora, Samson B. M. Chimphango, Alex J. Valentine, Claudine Elmerich, and William E. Newton (Eds). Springer, Volume 42, 2008 ISBN: 978-1-4020-8251-1

Valentine AJ, Kleinert A (2007) Phosphate deficiency affects respiratory metabolism of dark co2 fixation in mycorrhizal roots. Mycorrhiza 17: 137-143

Cloete KJ, Valentine AJ, Blomerus L, Botha A, Perez-Fernandez (2007) Nutritional effects of indigenous arbuscular mycorrhizal associations on the sclerophyll Agathosma betulina (Berg.) Pillans. Web Ecology 7: 77-86

Valentine AJ (2007) Comment on the multi-person interview: “The future of research universities”. EMBO Reports 8 (12): 1

Le Roux MR, Ward CL, Botha FC and Valentine AJ (2006) The route of pyruvate synthesis under Pistarvation in legume root systems. New Phytologist 169: 399-408

Valentine AJ, Kleinert A (2006) Respiratory metabolism of root-zone co2 in mycorrhizal plants with NH4+ and NO3– nutrition. Symbiosis Journal Vol. 41, No. 3 (2006), pp. 119-126

Valentine AJ, Mortimer PE, Lintnaar M, Borgo R (2006) Photosynthetic and nutritional responses of drought stressed arbuscular mycorrhizal grapevines. Symbiosis Journal Vol. 41, No. 3 (2006), pp. 127-134

Mortimer PE, Archer E and Valentine AJ (2005) Mycorrhizal C costs and nutritional benefits in developing grapevines. Mycorrhiza 15: 159-165

Meyer A, Valentine A, Botha A, Archer E and Louw K (2005) The occurence and infectivity of arbuscular mycorrhizal fungi in inoculated and uninoculated rhizosphere soils of two-year-old commercial grapevines. South African Journal of Enology and Viticulture 26 (2): 90-94

Van Rooyen M, Valentine AJ and Archer E (2004) The use of arbuscular mycorrhizal inoculants to decrease the transplant shock in young grapevines (Vitis species). South African Journal of Enology and Viticulture 25: nr 2, 37-45

Hengari SN, Valentine AJ and Theron JM (2004) The effect of the colonization extent of vesicular-arbuscular mycorrhizal fungi on the growth of pot grown Pterocarpus angolensis seedlings. South African Forestry Journal 202: 13-20

Meyer A, Valentine A, Botha A, Archer E and Louw K (2004) Young grapevine response and root colonisation following inoculation with arbuscular mycorrhizal fungi. SA Journal of Enology & Viticulture. Vol. 25(1), 26-32.

Viktor A, Cordero-Otero R and Valentine A (2003) Southern African legumes: a sustainable protein source. South African Journal of Science 99 (11/12 ): 1-5

Mortimer P, Jacobs GH, Valentine AJ and Cramer MD (2003) Water relations and photosynthetic response of protea bushes under irrigation. South African Journal of Botany , 69 (2): 135-143

Valentine A, Osborne B and Mitchell D (2002) Form of inorganic nitrogen influences mycorrhizal colonization and photosynthesis of cucumber. Scientia Horticulturae 92, 229-239

Valentine A, Osborne B and Mitchell D (2001) Interactions between phosphorus supply and total nutrient availability on mycorrhizal colonization, growth and photosynthesis of cucumber. Scientia Horticulturae 88, 177-189.

Current collaboration

Prof Maria Perez-Fernandez (Universidad Pablo De Olavida, Spain)
Prof Bill Plaxton (Queen’s University, Canada)
Prof Michael Udvardi (Noble Foundation, USA)
Dr Samson Chimpango (University of Cape Town, South Africa)
Prof Alf Botha (University of Stellenbosch, South Africa)
Prof Sehaam Kahn (CPUT, South Africa)
Prof Vagner Benedito (University of West-Virginia, USA)
Prof Georgina Hernandez-Delgado (Center for Genomic Sciences, Mexico)

Contact details

Plant-Microbe Interactions Group
Botany & Zoology Department
Faculty of Science
University of Stellenbosch
Private Bag X1
Matieland 7602
South Africa
Tel: (+27+21) 808-3067
Fax: (+27+21) 808-2405