Physiological and physical seed dormancy of some hypericum species growing in Turkey.

Cüneyt Çýrak1*, Ali Kemal Ayan2 and Kudret Kevseroglu1

1

Uni ver sity of Ondokuz Mayis, Fac ulty of Ag ri cul ture, De part ment of Agron omy, Samsun/Tur key

2

Uni ver sity of Ondokuz Mayýs, the High School of Pro fes sion of Bafra, Samsun/Tur key *Cor re spond ing au thor: Ad dress: Uni ver sity of Ondokuz Mayis, Fac ulty of Ag ri cul ture,

De part ment of Agron omy, 55139-Samsun, Tur key; Tel: +90-362-4576020; Fax: +90-362-4576034,

e-mail: cuneytc@omu.edu.tr

PHYSIOLOGICAL AND PHYSICAL SEED DORMANCY OF SOME

HYPERICUM SPECIES GROWING IN TURKEY

ABSTRACT

To in ves ti gate the na ture of dor mancy in Hypericum androsaemum, H. scabrum, H. lydum and H. tetrapterum seeds which did not show ger mi na tion un der nor mal lab o ra tory con di tions. The 15 day long ger mi na tion ex per i -ment un der the con stant light pre ceded by 30 min soak ing in wa ter (tap wa ter, 40, 50 and 60°C hot wa ter), GA₃ (50, 100 and 150 ppm) and H₂SO₄ (1, 2 and 3%) was per formed. The ger mi na tion re sponse to the presoak ing treat -ments was vari able and dis cussed as a pos si ble re sult of dou ble dor mancy in volv ing par tially dor mant em bryo and a chem i cal in hib i tor for H. androsaemum and H. scabrum. Seed ger mi na tion was re stricted only by hard seed coat in H. lydum, and H. tetrapterum indicating the presence of physical dormancy.

Key words: dou ble dor mancy, ger mi na tion, Hypericum androsaemum, H. lydum, H. scabrum, H. tetrapterum,,

pre-soak ing treat ments

INTRODUCTION

Hypericum spe cies are of great in ter est for man kind through out many cen tu ries

and have been used as tra di tional me dic i nal plants due to their wound-heal ing (Yazaki and Okuda, 1990), bactericide (Ishiguro et al., 1998), anti-in flam ma tory (Dias et al., 1998), di uretic and sed a tive prop er ties (Holz and Ostrowiski, 1987) for last two hun dred years. The Hypericum ge nus of Guttiferae is rep re sented in Tur -key by 89 spe cies of which 43 are en demic; the most abun dant and well known is H.

perforatum (Da vis, 1988).

Hypericum androsaemum L. grows in West Eu rope (Flora Europaea, 1968) and

in damp or shady places of Tur key (Da vis, 1988). In fu sion of H. androsaemum leaves has been used in tra di tional med i cine for its di uretic and antihepatotoxic ac -tiv i ties (Costa, 1994). Phe no lic com pounds, such as flavonoids, phe no lic ac ids and xanthones, are known to be pres ent in this spe cies (Schmidt et al., 2000) and have Communicated by Andrzej Anio³

P L A N T B R E E D I N G A N D S E E D S C I E N C E

Volume 53 2006

been re ported to be re spon si ble for its phar ma co log i cal prop er ties (Valentao et al., 2002). Hypericum scabrum L. is an her ba ceous pe ren nial plant which is dis trib uted in dry rocky slopes and open wood land of Tur key (Da vis, 1988) and has been used by Turk ish folk for its antispasmodic, sed a tive and anti-in flam ma tory prop er ties (Tanker, 1971). In Tur key, a skin rem edy is pre pared from its ae rial parts and it is used as an oint ment against pso ri a sis in folk med i cine. An ti bac te rial ac tiv i ties of

Hypericum scabrumhave been re ported by sev eral in vi tro stud ies (Azýrak and Erdoðrul, 2003). Al though there are sev eral in ves ti ga tions on the phytochemistry and bi o log i cal ac tiv ity of H. androsaemum and H. scabrum, lit tle ef fort has been ded i cated to the study of other as pects of these spe cies and there is, so far, no re port re lated to H. lydum Boiss and H. tetrapterum Fries grow -ing wild in rocky slopes and stream sides in Tur key. These spe cies of Hypericum have not been do mes ti cated yet in Tur key and due to un con trolled har vest ing as well as sea sonal, cli ma tic, and geo graphic re stric tions, the avail abil ity of wild plants from their na tive pop u la tions is strongly lim ited.

Ger mi na tion is a crit i cal stage in the life cy cle of weeds and crop plants, and of ten con trols pop u la tion dy nam ics, with ma jor prac ti cal im pli ca tions (Keller and Kollmann, 1999). Gen er ally ger mi na tion ca pac ity of Hypericum spe cies is very low due to seed dor mancy (Macchia et al., 1983) which is caused by a chem i cal in -hib i tor exudate from the cap sule in H. perforatum (Camp bell, 1985) and ab sence of light has a neg a tive ef fect on ger mi na tion in Hypericum spe cies (Çýrak et al., 2004a). Plant growth reg u la tors such as GA3 (gibberellic acid) and IAA (indoleacetic acid) (Iglesias and Babiano, 1997); chem i cal sub stances such as H2SO4 (sulphuric acid) (Baes et al., 2002) and hot wa ter treat ments (Hermansen et al., 1999) have been rec om mended in break ing dor mancy and to en hance ger mi na tion. The ob jec tives of this study were to de ter mine the ef fect of ex og e nously ap -plied GA3, H2SO4,hot and tap wa ter on ger mi na tion and to find an ef fec tive method for break ing seed dor mancy of H. androsaemum, H.scabrum, H. lydum and H. tetrapterum.

MATERIALS AND METHODS

The 10 month-old seeds of H. androsaemum, H.scabrum, H. lydum and H. tetrapterum wild plants grow ing in dif fer ent places of Black Sea geo graph ical re -gion of Tur key were used as a ma te rial. In pre lim i nary test, the seeds did not show ger mi na tion un der nor mal lab o ra tory con di tions (at 20 °C dur ing 21 days (Anon y -mous, 2005)), so they were soaked in 50, 100 and 150 ppm GA3; 1, 2 and 3% H2SO4 so lu tions, tap wa ter, 40, 50 and 60°C hot wa ter for 30 min utes and ger mi nated on Petri dishes un der con tin u ous il lu mi na tion (1200 lux white light) in growth cham bers at 20°C. Tap wa ter ap pli ca tion was treated as con trol and the ger mi na tion ca -pac i ties were cal cu lated as “per cent age”. Ger mi na tion of the seeds ex posed to dif fer ent pre-treat ments was eval u ated 15 days later. Three rep li ca tions (100 seeds each) of each pretreat ment were ob jected to ANOVA and dif fer ences among treat -ments were tested Duncan Mul ti ple Range Test (Level of sig nif i cance P<0.01).

RESULTS

The pre-soak ing treat ments tested in the pres ent study had a sig nif i cant (P<0.01) ef fect on ger mi na tion de pend ing on spe cies (Fig ure 1).

In H. androsaemum, GA3 treat ments were found to be most ef fec tive to im prove seed ger mi na tion while ger mi na tion was de te ri o rated by hot wa ter and H2SO4 when com pared to con trol. 150 and 100 ppm GA3 treat ments gave the high est ger mi na -tion for this spe cies with 29 and 24% re spec tively. These num bers were fol lowed by con trol with 20%.

In con trast to the other Hypericum spe cies eval u ated in this study, ger mi na tion re sponse of H. scabrum seeds to hot wa ter treat ments was pos i tive and sig nif i cant. The high est ger mi na tion for H. scabrum was ob tained from 40 °C hot wa ter treat -ment (21%) and this was fol lowed by 150 ppm GA3 and wa ter-soaked con trol with 19 and 14% re spec tively. Also, when com pared to con trol, H2SO4 treat ments were in ef fec tive to en hance ger mi na tion.

H2SO4 treat ments were the only ef fec tive ones in pro mot ing ger mi na tion for H. lydum and H. tetrapterum seeds. 2 and 3% H2SO4 treat ments re sulted in 11% ger mi na tion in H. lydum and 11 and 8.37% ger mi na tion in H. tetrapterum re spec -tively. The other treat ments were all gen er ally in ef fec tive in im prov ing ger mi na tion for both spe cies.

DISCUSSION

Light has been rec og nized since the mid-nine-tenth cen tury as a ger mi na -tion-con trol ling fac tor. In gen eral, Hypericum spe cies need light to ger mi nate at the

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H. scabrum H. lydum H. tetrapterum

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40°C hot water 50°C hot water 60°C hot water 50 ppm GA3 100 ppm GA3 150 ppm GA3 0.5 % H2SO4 1.0 % H2SO4 1.5 % H2SO4 Control

Fig. 1. The ger mi na tion ca pac i ties of H. androsaemum, H. scabrum, H. lydum and H. tetrapterum seeds ex posed to dif fer ent pre-soak ing treat ments. (Val ues with dif fer ent let ters within col umns

high est level (Ash et al., 1998; Çýrak et al., 2004a). There fore, this study was con -ducted out un der con tin u ous il lu mi na tion to sup ply this light re quire ment.

Seeds of many wild plants have hard seed coats which re strict wa ter ab sorp tion by the em bryo. Per me abil ity may be im proved by scar i fy ing the seed coat by me -chan i cal means (e.g. clip ping, abra sion or im mer sion in hot wa ter) or chem i cally with strong ox i da tive agents (e.g. sulphuric acid or so dium hypochlorite) (Abdallah et al., 1989). In the pres ent study, H2SO4 treat ments were found to be the most ef fec tive to in duce seed ger mi na tion for H. lydum and H. tetrapterum. The re sults in -di cate the pres ence of phys i cal dor mancy in both spe cies re lated to hard seed coat and over came by only acid scarification. How ever, it should be noted that the acid pretreat ment had a strong dam age on seed coat in H. androsaemum. The high ger -mi na tion ob tained with H2SO4 treat ments agree with those ob tained for other spe -cies like: Prosopis ferox (Baes et al., 2002), Aca cia origena, Aca cia pilispina and Pterolobium stellatum (Teketay, 1998).

Stud ies of ge net ics and phys i ol ogy have shown the im por tant roles of the plant hor mones like abscisic acid and gibberellin in the reg u la tion of dor mancy and ger -mi na tion (Koornneef et al., 2002). Gib ber el lins com prise the class of hor mones most di rectly im pli cated in the con trol and pro mo tion of seed ger mi na tion. These com pounds oc cur at rel a tively high con cen tra tions in de vel op ing seeds but usu ally drop to a lower level in ma ture dor mant seeds (Schwachtje and Baldwin, 2004). En -dog e nously ap plied gib ber el lins can re lieve cer tain types of dor mancy, in clud ing phys i o log i cal dor mancy, photodormancy and thermodormancy act ing as a sub sti -tute for low tem per a tures, long days, or red light (Seiller, 1998). In this study, GA3 in creased ger mi na tion sig nif i cantly de pend ing on doses in H. androsaemum and H. scabrum in di cat ing the pres ence of phys i o log i cal dor mancy re lated to par tially dor -mant em bryo for both spe cies. The ger mi na tion en hanc ing ef fect of GA3 was re -ported from the stud ies car ried on other spe cies such as Sesamum indicum (Kyauk et al., 1995), Zea mays and Glycine max (Wang et al., 1996).

Pre vi ous re searches with hot wa ter treat ments to in duce ger mi na tion were in con -sis tent and vari able. Some of them have re ported hot wa ter treat ments to en hance ger mi na tion of hard coated seeds by el e vat ing wa ter and O2 per me abil ity of testa. Hermansen et al. (1999) re ported that ger mi na tion was en hanced by presoking in 44, 49 and 54°C hot wa ter for 5-40 min utes in car rot seeds and dip ping seeds in boil ing wa ter for 1–60 s. was very ef fec tive in pro mot ing ger mi na tion for Dodonea viscosa (Da vis et al., 2004). On the con trary, no sig nif i cant seed ger mi na tion re -sponse to hot wa ter treat ments has been re ported for some Aca cia spe cies (Masamba, 1994) and Myrtus communis (KhoshKhui and Bassiri 1976). Sim i -larly, in the pres ent study the ef fects of hot wa ter treat ments on seed ger mi na tion of the Hypericum spe cies tested were change able and H. scabrum was the only spe -cies show ing pos i tive ger mi na tion re sponse to hot wa ter treat ments in di cat ing the pres ence of phys i cal dor mancy.

Chem i cals that ac cu mu late in fruit and seed cov er ing tis sues dur ing de vel op ment and re main with the seed af ter har vest can be shown to act ger mi na tion in hib i tors. Some of the sub stances as so ci ated with in hi bi tion are var i ous phe nols, coumarin and abscisic acid and can be leached out of the seeds by soak ing in wa ter. For ex am -ple, in a pre vi ous study on Hypericum perforatum we ob served that the chem i cal

in hib i tor in exudate from cap sule could be elim i nated effectively by a sim ple soak ing in tap wa ter (Çýrak et al., 2004b). In this study, sim i larly, the col our of the wa ter in which both seeds were soaked turned yel low ish and wa tersoaked con -trol re sulted in higher ger mi na tion in H. androsaemum and H. scabrum. The re sults sug gested that seeds of both spe cies in clude some chem i cal in hib i tors can be leached by soak ing in tap wa ter.

CONCLUSION

Con se quently, the re sults from the pres ent study showed that the ef fects of dif fer -ent pre-soak ing treat m-ents on seed ger mi na tion of tested Hypericum spe cies were sig nif i cant de pend ing on spe cies. GA3 and wa tersoaked con trol were the most ef -fec tive treat ments to im prove ger mi na tion of H. androsaemum, sug gest ing that the seeds ex hibit both phys i o log i cal dor mancy in volv ing a par tially dor mant em bryo and chem i cal dor mancy as so ci ated with a chem i cal in hib i tor. For H. scabrum, all treat ments were gen er ally ef fec tive in pro mot ing ger mi na tion. But hot wa ter and GA3 treat ments in creased ger mi na tion mainly. It can be con cluded that H. scabrum seeds, like those of H. androsaemum, ex hibit dou ble dor mancy: the phys i cal dor mancy in volv ing a hard seed coat and the phys i o log i cal dor mancy re lated to a par -tially dor mant em bryo. H2SO4 treat ments were the only ef fec tive ones in pro mot ing ger mi na tion for H. lydum and H. tetrapterum seeds. In con trast to H. androsaemum and H. scabrum, seed ger mi na tion was re stricted only by hard seed coat in H. lydum and H. tetrapterum in di cat ing the pres ence of phys i cal dor mancy.

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