Mycorrhizal fungi form the most important mutualistic symbioses on earth with plants. Much research has shown that the development of arbuscular mycorrhize (AM) is correlated with plant secondary metabolism. AM fungi can directly or indirectly affect plant secondary metabolic processes. Camptothecin (CPT), a secondary metabolite in a special Chinese tree Camptotheca acuminata, has gained great attention for its remarkable inhibitory activity against tumor cells. The effect of AM infected with six fungi belonging to two genera on CPT content in C. acuminata seedlings was carried out in the present study.
The selected sterile seeds of C. acuminata were sown in sterilized sands in the greenhouse. After 70 days of cultivation，seedlings with similar height and crown were selected and divided into seven groups (10 pots per group). Each group of C. acuminata seedlings was inoculated with one of AM fungus Glomus manihot, G. versiforme, G. etunicatum, G. diaphanum, Acaulospora mellea, A. laevis, or non-mycorrhizal inoculation, namely Gm, Gv, Ge, Gd, Am, Al, or control (CK), respectively. After 3-month cultivation, the symbiotic association was observed and CPT content in the seedlings of C. acuminata was determined.
All C. acuminata seedlings inoculated with six fungi formed AM. Colonization rates of AM was over 70% in seedlings infected with 4 Glomus fungi (Gm, Gv, Ge, Gd), and ～50% with 2 Acaulospora fungi. Mycorrhizal colonization intensity of roots (M) and infected root fragments (m) were showed in Table 1. Good symbiosis systems were formed between C. acuminata seedlings and selected mycorrhizal fungi.
In roots, CPT contents in mycorrhizal seedlings were significantly higher than non-mycorrhizal seedlings, except Gm. CPT contents in Gd, Am, Al, Ge and Gv were 2.5, 2.1, 1.7, 1.6, and 1.3 times higher as CK, respectively. In the stem, CPT content was significantly higher in Al than CK, no significant difference among CK, Ge, Gd, and Am, while significantly lower in Gm and Gv than CK. In leaves, CPT contents in Al, Gd and Am were 60%, 40% and 40% higher than CK, respectively, however, CPT contents in Gm, Gv and Ge was affected little by the AM infection. CPT contents in the whole plant in Gd, Al, Am and Ge were 150%, 150%, 140% and 120% of CK, respectively, no remarkable difference between Gv and CK, whereas 23% lower in Gm than CK. As a whole, AM infection was beneficial to CPT accumulation in C. acuminata seedlings with G. diaphanum, G. etunicatum, A. laevis, and A. mellea, no influence with G. versiforme, and reduced with G. manihot .
AM also changed CPT allocation in different organs of C. acuminata seedlings. CPT ratios in all mycorrhizal roots were higher than non-mycorrhizal seedlings. In mycorrhizal root of Gv CPT ratio was the highest, 32% out of the whole plant, comparing with 15% in CK. Due to the increase of CPT allocation in roots, CPT was less distributed in stems and leaves in mycorrhizal seedlings.